Can anyone help me Algebra 2 question

The question says to solve for x and state any restrictions for the variable

ax + bx + 9 = 7

another one is

a(bx + 2) = cx - 12

If anyone can tell me what is means by restrictions on th variables or if you want to help me solve it

ax + bx + 9 = 7
x(a+b) = -2
x = -2/(a+b)
Restriction: (a+b) can't =0

another one is

a(bx + 2) = cx - 12
abx+2a = cx-12
abx-cx = -12-2a
cx-abx = 2(a+6)
x(c-ab) = 2(a+6)
x = 2(a+6)/(c-ab)
same as 1st (c-ab) cant = 0

ax + bx + 9 = 7
ax + bx = -2
x(a+b) = -2
x = -2 / (a+b)