Plz explain. I am confused

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

Which equation can be used to measure the density of water in a spherical water tank? let w represent the number of water particles within the region.

Olivia is using 160 quilt squares to make a red, yellow, and blue quilt if 25% of the quilt are red and 30% are yellow how many quilt squares are blue