To earn money for her new computer, Tina sells handmade postcards. In a day, she can make 30 such postcards. For each postcard sold, Tina gets $5. How much money did Tina earn if she managed to sell all the postcards she made every day for 6 days? Give the rationale and then the answer.
Let's think step by step. Tina made postcards for 6 days, so she has made 6 days * 30 postcards / day = 180 postcards. For every postcard, Tina gets $5, so if she sold every card, she got 180 postcards * $5 / postcard = $900.. The answer is: 900.

Tom reads 10 hours over 5 days. He can read 50 pages per hour. Assuming he reads the same amount every day how many pages does he read in 7 days? Give the rationale and then the answer.
Let's think step by step. He reads 10 / 5 = 2 hours per day. That means he reads 2 * 50 = 100 pages per day. So he reads 100 * 7 = 700 pages in 7 days.. The answer is: 700.

At the patisserie, a single layer cake slice is $4 and a double layer cake slice is $7. Dusty buys 7 single layer cake slices and 5 double layer cake slices. If he pays with a $100 bill, how much change does he receive? Give the rationale and then the 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.
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Let's think step by step. Single layer cake slices cost $4 x 7 = $28. Double layer cake slices cost $7 x 5 = $35. All the cake slices together cost $28 + $35 = $63. He will receive change of $100 - $63 = $37.. The answer is: 37.