Answer is A. You start by adding the 7 to the opposite side. Giving you 19. You divide both sides by -2 which gives you x on one side and -9.5 on the other.
Move the decimal so there is one non-zero digit to the left of the decimal point. The number of decimal places you move will be the exponent on the
10
.If the decimal is being moved to the right, the exponent will be negative. If the decimal is being moved to the left, the exponent will be positive.