Let the speed of the faster bike = X
The slower bike would be x - 4 ( 4 mph slower)
Multiply each speed by time and add to equal total distance:
2x + 2(x-4) = 56
Simplify:
2x + 2x -8 = 56
4x -8 = 56
Add 8 to each side:
4x = 64
Divide both sides by 4:
x = 64/4
x = 16
The faster bike rode at 16 miles per hour
The slower bike traveled at 16-4 = 12 miles per hour