I really need help with this one

Perform the required operations on the following functions given: f(x)= 3-x; g(x)= -2x find g[f(x)]

Find the x-intercept and y-intercept of the line. 3x + 5y = −15

Can someone factor this fully? my friend and i have two different answers and i would like to know if either of them is right. you in advance. a^2 - b^2 + 25 + 10a