21=-9(y+5)+6(y+8)

Solution for 21=-9(y+5)+6(y+8) equation:

Simplifying
21 = -9(y + 5) + 6(y + 8)

Reorder the terms:
21 = -9(5 + y) + 6(y + 8)
21 = (5 * -9 + y * -9) + 6(y + 8)
21 = (-45 + -9y) + 6(y + 8)

Reorder the terms:
21 = -45 + -9y + 6(8 + y)
21 = -45 + -9y + (8 * 6 + y * 6)
21 = -45 + -9y + (48 + 6y)

Reorder the terms:
21 = -45 + 48 + -9y + 6y

Combine like terms: -45 + 48 = 3
21 = 3 + -9y + 6y

Combine like terms: -9y + 6y = -3y
21 = 3 + -3y

Solving
21 = 3 + -3y

Solving for variable 'y'.

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

Add '3y' to each side of the equation.
21 + 3y = 3 + -3y + 3y

Combine like terms: -3y + 3y = 0
21 + 3y = 3 + 0
21 + 3y = 3

Add '-21' to each side of the equation.
21 + -21 + 3y = 3 + -21

Combine like terms: 21 + -21 = 0
0 + 3y = 3 + -21
3y = 3 + -21

Combine like terms: 3 + -21 = -18
3y = -18

Divide each side by '3'.
y = -6

Simplifying
y = -6