Question 1086473
Let n-15 be Lisa's first speed, and n be her second speed. Then:
60/(n-15) +1=135/n
60n+n²-15n=135(n-15)
n²-90n+2025=0
(n-45)²=0
n=45
n-15=30
60/30=2
135/45=
135+60 miles/2+3 hours=39 mph avg
☺☺☺☺