If average of 3 quantities is 15 , sum of quantities is?

Idon’t understand this.. will someone ? will mark brainliest along with 20 points.

Consider the following equation -167 + 37 = 49 - 21p select the equation that has the same solution as the given equation. o a. p - 5 + ip = 7 - p ob. +55 + 12p = 5p + 16 c. 2 + 1.25p = -3.75p + 10 d. -14 + 6p = -9 - 6p reset next

Ineed i been stuck on this question since yesterday