7.
y + 8x = -2
f(x) = y = -8x - 2
f(0)=-2, f(1)=-10, f(2)=-18, f(-2)=14
8.
12x + 3y = 15
3y = -12x + 15
f(x) = y = -4x + 5
f(-1)=9, f(0)=5, f(1)=1
9.
y - 3x = 9
f(x) = y = 3x + 9
f(-2)=3, f(0)=9, f(2)=15
10.
0.4y + 2x = 1.2
4y + 20x = 12
4y = -20x + 12
f(x) = y = -5x + 3
f(-3) = 18, f(0)=3