f(x)=7-8x; x=-2, x=4
f(x)=-8x+7
f(-2)=-8(-2)+7 f(4)= -8(4)+7
f(-2)= 16+7 f(4)= -32+7
f(-2)=23 f(4)= -25
f(x)=7-8x, f(2)=24f(x)=7-8x, f(4)=-25
