(7t+21)+(t+4)=15

Solution for (7t+21)+(t+4)=15 equation:

Simplifying
(7t + 21) + (t + 4) = 15

Reorder the terms:
(21 + 7t) + (t + 4) = 15

Remove parenthesis around (21 + 7t)
21 + 7t + (t + 4) = 15

Reorder the terms:
21 + 7t + (4 + t) = 15

Remove parenthesis around (4 + t)
21 + 7t + 4 + t = 15

Reorder the terms:
21 + 4 + 7t + t = 15

Combine like terms: 21 + 4 = 25
25 + 7t + t = 15

Combine like terms: 7t + t = 8t
25 + 8t = 15

Solving
25 + 8t = 15

Solving for variable 't'.

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

Add '-25' to each side of the equation.
25 + -25 + 8t = 15 + -25

Combine like terms: 25 + -25 = 0
0 + 8t = 15 + -25
8t = 15 + -25

Combine like terms: 15 + -25 = -10
8t = -10

Divide each side by '8'.
t = -1.25

Simplifying
t = -1.25