Two planes, which are 2480 miles apart, fly toward each other. Their speeds differ by 70 mph. if they pass each other in 4 hours, what is the speed of each?
Let the speed of the slower plane be $x$ mph. The speed of the faster plane is then $x+70$ mph.
We know that distance equals rate times time, so the slower plane travels $4x$ miles and the faster plane travels $4(x+70)$ miles. Because they passed each other, we can add these distances together to get $4x+4(x+70)=8x+280=2480$.
Subtracting 280 from both sides gives $8x=2200$, and dividing both sides by 8 gives $x=275$. Therefore, the slower plane travels at a speed of $\boxed{275}$ mph, and the faster plane travels at a speed of $275+70=\boxed{345}$ mph.