For this case we can make the following rule of three:
4400 -------> 100%
2200 -------> x
From here, we clear the value of x.
We have then:
x = (2200/4400) * (100)
x = 50%
Answer:
The main span of bridge at (2200 feet) is 50 percent shorter than the main span of bridge b (4400 feet)
