How do I find this formula?

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

The u-drive rent-a-truck company plans to spend $13 million on 320 new vehicles. each commercial van will cost $25 comma 000, each small truck $50 comma 000, and each large truck  $80 comma 000. past experience shows that they need twice as many vans as small trucks. how many of each type of vehicle can they buy?

What is the value of x in this triangle? a. 53° b. 62° c. 65° d. 118°