This triangle is obtuse( as it's one angle is greater than 90°) as well as isosceles (as it's two sides are equal).
total bill before any discounts $13.
she is a student, so she gets 20% off.
she brought an item of clothing, so she gets 5% off.
so she's really getting 20% + 5% off, namely 25% off her bill.

Step-by-step explanation:
3(-8m-1) + 5(m+8) (remove the parentheses)
-24m - 3 + 5m + 40 (collect like terms and calculate)
-19m + 37