[Question]Joe goes camping with his dad on a Friday. Joe's dad has 21 marshmallows, and Joe has four times as much marshmallows as his dad. If Joe’s dad roasts a third of his marshmallows, and Joe roasts half of his marshmallows, how many marshmallows did they roast in total?
[Answer]Joe’s dad roasts 21 / 3 = 7 of his marshmallows. Joe has 21 * 4 = 84 marshmallows. Joe roasts 84 / 2 = 42 of his marshmallows. Joe and his dad roasted 7 + 42 = 49 marshmallows in total. The answer is 49.

[Question]Matthew drinks 4 glasses of water per day. Each glass is 5 ounces. He decides to just buy a 35 ounces water bottle. How many times will he fill it each week?
[Answer]He drinks 20 ounces of water a day because 4 x 5 = 20. The drinks 140 ounces in a week because 7 x 20 = 140. He will fill it up 4 times because 140 / 35 = 4. The answer is 4.

[Question]Tony exercises every morning by walking 3 miles carrying a 25-pound backpack, then he runs another 10 miles without the backpack. If he walks at a speed of 3 miles per hour and runs at a speed of 5 miles per hour, how many hours each week does he spend exercising?
[Answer]Tony walks 3 miles at 3 miles per hour for 3 / 3 = 1 hour. Tony also runs 10 miles at 5 miles per hour for 10 / 5 = 2 hours. Thus, each day he exercises for 1 + 2 = 3 hours. Over the course of one week, he exercises for 3 * 7 = 21 hours. The answer is 21.

[Question]Javier is an Olympic javelin thrower. In the last Olympics, he threw the javelin three times. The first throw, he threw the javelin twice as far as he threw the javelin on his second throw, but only half as far as he threw it the third throw. If the sum of all three throws was 1050 meters, then how far, in meters, did he throw the javelin on his first throw?
[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
Let x be the distance he threw the javelin on the first throw. Thus, the sum of his three throws is x + 0.5x + 2x = 1050 meters. Thus, 3.5x = 1050. And we find the distance he threw the javelin on the first throw is x = 300 meters. The answer is 300.