Can someone me in this algebra question 100% correct only

Find the average rate of change for f(x) = x2 − 3x − 10 from x = −5 to x = 10.

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?

If mary had 320 toy cars and she gave her friend 50 cars and then she gave her brother 72 more cars how much toy cars would mary have left ● explain with proper details