If 21 is added to a number, the result is 37 less than twice the number. find the number?

Let's give "the number" a variable like x. Now break the problem apart. First 21 is added to x.

X+21

The result is 37 less ( -37) than twice (2x)

2x-37

So by putting them together we'll have the equation

X+21=2x-37
X=58

The answer is 225 miles per 4.5 hours. hope this ; )