Write the arithmetic series in summation notation 4+8+12+16

I’ve been trying all day to figure this puzzle out. i need the work for it aswell. it is a factoring polynomials tarsia. the image is below.

Bobs burgers bam has a special deal of 4 hamburgers for $6. at that rate, how much should it cost to buy 3 hamburgers?

Given the diagram below, michael writes, "segment ac is congruent to segment ac." which of the following reasons allow him to write this statement?