It's the 3rd equation (which is in a disguised form)...we have
90 - 10y = 5x add 10y to both sides
90 = 5x + 10y
This says that the nmber of tmes she hiked the 5 mile trail (x) plus the number of times she hiked the 10 mile trail (y) = 90 miles
9.5m questions
12.2m answers