If f(x)=2x+1f(x) = 2x + 1f(x)=2x+1, what is xxx when f(x)=9f(x) = 9f(x)=9?
x=4x = 4x=4
x=5x = 5x=5
x=3x = 3x=3
x=10x = 10x=10