A little Help please

At 6:00 pm the temperature was -5°F outside. By midnight the temperature had dropped 12 degrees. What was the temperature at midnight?

A. -7°F

B. -17°F

C. 17°F

Thanks!

In triangle △abc, ∠abc=90°, bh is an altitude. find the missing lengths. ah=4 and hc=1, find bh.

How can i differentiate this equation?

Arestaurant offers delivery for their pizzas. the total cost the customer pays is the price of the pizzas, plus a delivery fee. one customer pays $23 to have 2 pizzas delivered. another customer pays $59 for 6 pizzas. how many pizzas are delivered to a customer who pays $86?