-2t-(t-3)=21

Solution for -2t-(t-3)=21 equation:

Simplifying
-2t + -1(t + -3) = 21

Reorder the terms:
-2t + -1(-3 + t) = 21
-2t + (-3 * -1 + t * -1) = 21
-2t + (3 + -1t) = 21

Reorder the terms:
3 + -2t + -1t = 21

Combine like terms: -2t + -1t = -3t
3 + -3t = 21

Solving
3 + -3t = 21

Solving for variable 't'.

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

Add '-3' to each side of the equation.
3 + -3 + -3t = 21 + -3

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

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

Divide each side by '-3'.
t = -6

Simplifying
t = -6