-21=-9d+7d

Solution for -21=-9d+7d equation:

Simplifying
-21 = -9d + 7d

Combine like terms: -9d + 7d = -2d
-21 = -2d

Solving
-21 = -2d

Solving for variable 'd'.

Move all terms containing d to the left, all other terms to the right.

Add '2d' to each side of the equation.
-21 + 2d = -2d + 2d

Combine like terms: -2d + 2d = 0
-21 + 2d = 0

Add '21' to each side of the equation.
-21 + 21 + 2d = 0 + 21

Combine like terms: -21 + 21 = 0
0 + 2d = 0 + 21
2d = 0 + 21

Combine like terms: 0 + 21 = 21
2d = 21

Divide each side by '2'.
d = 10.5

Simplifying
d = 10.5