Solve the Formula for the Specified Variable $a + b = s + r$

Multiple Choice

Solve the formula for the specified variable.
- $a + b = s + r$ for $r$

A) $r = a + b - s$
B) $r = s ( a + b )$
C) $r = \frac { a } { s } + b$
D) $r = \frac { a + b } { s }$