Answer:
300 + r = 217
Explanation:
300 -> 300
added to r -> +
is the same as -> =
217 -> 217
Put this in one equation and you get:
300 + r = 217
If you need to solve for r (need to isolate r to solve for r):
300 + r = 217
r = 217 / (-300)
r = -0.723333333