There are 1000 m in one km, so
5.06 km • 1000m/km = 5060 m
Unfortunately, this item does not come with any figure to illustrate the lengths of the rectangle. However, it may be noted that by connecting two opposite vertices of a rectangle by a diagonal, we form a right triangle. We may then use the Pythagorean theorem to solve for the answer.
a² + b² = c²
c in this equation is the length of the diagonal, a and b are the lengths of the sides.
20% of 89.75 is 17.95

so :

the Trina's coupon will subtract the answer by 10%:
10%of 71.8 is 7.18

so the final answer is:

she has to pay $64.62
hope this helps