Please help :0
Which of the following equations represents f(x)=x^4stretched vertically by a factor of 2 and horizontally by a factor of 4?

a.) f(x)=1/4(2x)^4
b.)f(x)=4(2x)^4
c.)f(x)=2(1/4x)^4
d.)f(x)=2(4x)^4