21=4-r

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Solution for 21=4-r equation:


Simplifying
21 = 4 + -1r

Solving
21 = 4 + -1r

Solving for variable 'r'.

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

Add 'r' to each side of the equation.
21 + r = 4 + -1r + r

Combine like terms: -1r + r = 0
21 + r = 4 + 0
21 + r = 4

Add '-21' to each side of the equation.
21 + -21 + r = 4 + -21

Combine like terms: 21 + -21 = 0
0 + r = 4 + -21
r = 4 + -21

Combine like terms: 4 + -21 = -17
r = -17

Simplifying
r = -17

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