I don’t understand one of my math questions, The total cost of a garden tractor priced $1,178.99 is $1,265.06. What is the sales tax rate? A. 0.7% B. 7.3% C. 8.6% D. 0.9% Can you explain how you did it too?

4. Glenn Andrews recently bought a new motorbike for $3,950. If he had to pay 6 percent sales tax on the bike, what was the total cost of the bike? A. $3,713 B. $4,010 C. $4,187 D. $2,370 5. Moneys taken out of a salary for such things as taxes, medical insurance, and retirement funds [...]

The John Deere Company has found that the revenue from sales of heavy-duty tractors is a function of the unit price p (in dollars) that it charges. If the revenue R is R(p)= -1/2p*2+1900p What unit price p (in dollars) should be charged to maximize revenue? What is the maximum revenue? PS: (*) means exponent