In the function y-1=(4x)^2+7 , what effect does the number 4 have on the graph, as compared to the graph of y=x^2 ?

a. it stretches the graph vertically by a factor of 4.

b. it shrinks the graph horizontally to 1/4 the original width.

c. it shrinks the graph vertically to 1/4 the original height.

d. it stretches the graph horizontally by a factor of 4.

***idk what this one means : / explain : ) ! : d