Question 800728
let Maria live x miles from the mountains

Let her rate to mountains be y

t=d/r

x/y = 9
x=9y

Return trip 4 hours
rate = y+40

x/(y+40) =4

substitute x
9y/(y+40)=4

9y=4y+160

9y-4y=160
5y=160
y= 160/5
y=32

x=9y
x=9*32= 288 miles

distance to the mountain = 288 miles