Answer:
16
notice how a right triangle was formed, and the Pythagorean theorem could be used to solve this :
a^2 + b^2 = c^2
a^2 + 15^2 = 17^2
a^2 + 225 = 289
a^2 = 64
a= 8
multiply it by 2 to get the side of the base
8 * 2 = 16
1. Rational/The sum of two rationals is always rational
2. Irrational/ the sum of a rational and an irrational is always irrational
3. Irrational/The product of a nonzero rational and an irrational is always irrational
4. Rational/The product of two rationals is always rational
Pretty much all the irrational numbers are the ones with radical signs over them and the rational numbers are the fractions and whole numbers. Once you identify the two numbers to be rational or irrational, you can then find your answer within the second part of the answers.
Division can be used. For example
50/16=3.125gallons
or you could use multiplication
50*1/16=3.125gallons
121 is big enough to assume normality and not worry about the t distribution. By the 68-95-99.7 rule a 95% confidence interval includes plus or minus two standard deviations. So 95% of the cars will be in the mph range

The question is a bit vague, but it seems we're being asked for the 95% confidence interval on the average of 121 cars. The 121 is a hint of course.
The standard deviation of the average is in general the standard deviation of the individual samples divided by the square root of n:

So repeating our experiment of taking the average 121 cars over and over, we expect 95% of the averages to be in the mph range

That's probably the answer they're looking for.