so she walked during this time with 4 miles per hour (x*4)
during
the rest of the way (which is 0.7-x, as the whole way took her 42
minutes, so the rest is 0.7-x) she walked with 5 miles per hour - the
distance was (0..7-x)*5 m/h
the total distance was 3 miles, so if we sum the two distances, we will get 3 miles:
x*4+ (0.7-x)*5=3
let's remove the bracket:
4x+0.7*5-5x=3
4x+3.5-5x=3
subtract 3.5 from both sides:
4x-5x=3-3.5
-x=-0.5
multiply both sides by (-1)
x=0.5:
so she walked for half an hour alone, that is for 30 minutes!
