15+8x=2x+7-5x
Subtract 8x from both sides.
15=2x+7-5x-8x
Combine like terms.
15=-11x+7
Subtract 7 from both sides.
8=-11x
Divide -11 from both sides.
.73=x
Your answer is .72

This result is actually true for any exterior angle. The exterior angle of a triangle is equal to the sum of the two remote angles, and above is a short proof of it.
question a is divide. 48 divided by -8 is -6.
question b is divide. -40 divided by 8 is -5.
question c is subtract. The negative sign on the 2 and the minus symbol cancel out.
question d is add. If you put a minus sign, the signs would cancel out and become addition.
question e is add. If you put a minus sign, the signs would cancel out and become addition.
question f is multiply. Half of 22 is 11 and the 0.5 is negative.