-2(10-s+1)=-21

Solution for -2(10-s+1)=-21 equation:

Simplifying
-2(10 + -1s + 1) = -21

Reorder the terms:
-2(10 + 1 + -1s) = -21

Combine like terms: 10 + 1 = 11
-2(11 + -1s) = -21
(11 * -2 + -1s * -2) = -21
(-22 + 2s) = -21

Solving
-22 + 2s = -21

Solving for variable 's'.

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

Add '22' to each side of the equation.
-22 + 22 + 2s = -21 + 22

Combine like terms: -22 + 22 = 0
0 + 2s = -21 + 22
2s = -21 + 22

Combine like terms: -21 + 22 = 1
2s = 1

Divide each side by '2'.
s = 0.5

Simplifying
s = 0.5