Please help I don’t understand

The function a represents the cost of manufacturing product a, in hundreds of dollars, and the function b represents the cost of manufacturing product b, in hundreds of dollars. a(t) = 5t + 2 b(t) = 7t - 2t +4 find the expression that describes the total cost of manufacturing both products, a(t) + b(t). a. 7t^2 - 7t + 2 b. 7t^2 + 3 +6 c. 7t^2 + 7t - 6 d. 7t^2 - 3t + 6

Janet drove 300 miles in 4.5 hours. write an equation to find the rate at which she was traveling

What number should be added to the expression x^2+3x+ in order to create a perfect square trinomial? 3/2 3 9/4 9