The (small) challenge here is to determine what the LCD is. Since 11, 17 and 3 are all prime, we find the LCD by multiplying them together: 561.
Then 9/11= 459/561; 15/17 = 495/561; and 2/3 = 375/561.
I say 12 because that would mean the first rectangle is 6x12 and the second is 10x12
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.
