One plane can travel 30 miles per hour faster than another. one of them goes 185 miles in the same time it takes the other to go 170 miles. what are their speeds

Plane #1 speed:  x mph
Plane #2 speed:  (x+30) mph

time = time becomes

170 mi        185 mi
=
      x             x+30

Solving for x, the speed of the slower plane, we get

170x + 5100 = 185 x
                                           5100
Then 15x = 5100, and x = (mi/hr) = 340 mph
                                              15

The slower plane flies at 340 mph, and the faster one at 370 mph.