问一道SAT数学题.

题目

问一道SAT数学题.
If v and x are positive integers such that v=7/3 b b=x²2
what is the least possible value of
A 14
B 21
C 28
D 35
E 42

答案

v、x 都是正整数,且v、x的关系为v=7/3 b b=x²2,消去b得：v=7x²/6
x=6最小,为42