I need a solution to these with explanations, I'm completely stuck on it

Question

The matrices below show the number of pizzas sold in each size at a local pizzeria last weekend. The cost for each size is also represented in a matrix.

Find the product of the matrices. Give the values of a, b, and c and interpret what each one represents.

Answer 1

28(8) +30(10)+ 25(12) = 224 +300+300 = a = $824 total pizza sales on Friday

26(8) +32(10) +30(12) = 208 +320 +360 = b = $888 total pizza sales on Saturday

18(8) + 24(10) + 25(12) = 144 +240 +300 = c = $684 total pizza sales on Sunday