Answer:
a. 100 mph
b. 500 mph
Explanation:
a.
Let the speed of Lindbergh's plane be x.
Today's planes are 5 times faster, so their speed is 5x.
Today's planes speed is 400 mph faster than Lindbergh's speed.
x + 400 = 5x
5x = x + 400
4x = 400
x = 100
Lindbergh's speed was 100 mph
b. 5x = 5 * 100 = 500
Today's planes fly at 500 mph