34 = 6x + 12.5y
3.5 = x + y
From the second equation you can find either x or y
x = 3.5 - y
Then you substitute x in the first equation with 3.5 - y
34 = 6(3.5 - y) + 12.5y
34 = 21 - 6y + 12.5y
13 = 6.5y
y = 2
So if y = 2 ...
3.5 = x + 2
x = 1.5
So she ran for 1.5 hours and biked for 2 hours
