co·ef·fi·cient
ˌkōəˈfiSHənt/Submit
noun
1.
MATHEMATICS
a numerical or constant quantity placed before and multiplying the variable in an algebraic expression (e.g., 4 in 4x y).
So your answer is 3
3 because the number 3 in 3x is a coefficient and the x is the variable.
hope that helps :)
