[Question]The number of trees is three times more than the number of stones in the courtyard. There are also twice as many birds in the trees as the combined number of trees and stones in the yard. If the number of stones is 40, how many birds are in the trees?
[Answer]The number of trees is three times more than the number of rocks, meaning there are 3 * 40 = 120 more trees than rocks in the courtyard. The total number of trees in the yard is 120 + 40 = 160. Combined, there are 160 + 40 = 200 trees and stones in the courtyard. Since the number of birds is twice the combined number of trees and stones in the courtyard, there are 2 * 200 = 400 birds on the trees. The answer is 400.

[Question]Donna made a cake to take to a party where the guests ate half the cake. The day after the party, she shared half the leftovers with her brothers. The following day, she ate one piece as a midnight snack. Twice as many pieces as her snack were left. How many pieces was the cake to begin with?
[Answer]Donna had 2 * 1 = 2 pieces of cake left. Before her snack, there were 2 + 1 = 3 pieces left. Those 3 pieces were half the leftovers, so she had 3 * 2 = 6 pieces before sharing with her brothers. Those 6 pieces were half the party leftovers, so the cake was 2 * 6 = 12 pieces before the party. The answer is 12.

[Question]John decides to take up illustration. He draws and colors 10 pictures. It takes him 2 hours to draw each picture and 30% less time to color each picture. How long does he spend on all the pictures?
[Answer]The coloring takes 2 * .3 = .6 hours less than the drawing. So it takes 2 - .6 = 1.4 hours per picture. So it takes him 2 + 1.4 = 3.4 hours per picture. That means it takes 3.4 * 10 = 34 hours. The answer is 34.

[Question]Michael has 4 packs of crayons and wants to buy 2 more. One pack of crayons costs $2.5. How much are all the packs of crayons Michael will have after the purchase worth?
[Answer]

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
After buying 2 more packs, Michael is going to have 4 packs + 2 packs = 6 packs of crayons. In total all packs are going to be worth 6 packs * $2.5 / pack = $15. The answer is 15.