Answer:
r=21+y
Step-by-step explanation:
its telling you that r is going to be equal to the rest of the equation, so we start with
r=
then, it mentions the sum of 21 and y, so this would be represented as
21+y
since r is equal to the sum of 21 and y, your answer is
r=21+y
(because of comutitive property, r=y+21 is also an acceptable answer.)
