solve for s: -7=+-3s

-7 = + -3S (orig problem)

-7 = -3S (simplify)

-3S = - 7 (transpose to get S to left side)

3S = 7 (multiply both side by -1)

S = 7/3 (divide both side by 3)

S = 2 1/3, or 2.33333... (divide 7 by 3 and show as compound fraction and decimal)