The task is to generate the correct answer for a given math problem.

[Q]: Problem: if x , y , and z are positive integers , and 3 x = 5 y = 6 z , then the least possible value of x + y + z is
[A]: 21


[Q]: Problem: a question paper has 2 parts , a & b , each containing 8 questions . if a student has to choose 8 from part a & 4 from part b , in how many ways can he choose the questions ?
[A]: 70


[Q]: Problem: peter invests a sum of money and gets back an amount of $ 815 in 3 years . david invests an equal amount of money and gets an amount of $ 850 in 4 years . if both amounts were invested at the same rate ( simple interest ) what was the sum of money invested ?
[A]:
71