-21=7(8+r)

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Solution for -21=7(8+r) equation: 



-21=7(8+r)

We move all terms to the left:

-21-(7(8+r))=0

We add all the numbers together, and all the variables

-(7(r+8))-21=0



We calculate terms in parentheses: -(7(r+8)), so:

7(r+8)

We multiply parentheses

7r+56

Back to the equation:

-(7r+56)



We get rid of parentheses

-7r-56-21=0

We add all the numbers together, and all the variables

-7r-77=0

We move all terms containing r to the left, all other terms to the right

-7r=77

r=77/-7

r=-11

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