Factors of polnomial 7x+49 of the polymial 7x + 49

How is this equation completed? i cannot find any examples in the book.

Given a = {(1, , 5)(6,4)}, b = {(2,0)(4, ,5)(0, 0)) and c = {(1, 1)(0, 2)(0, 3)(0, ,5)}, answer the following multiple choice question: from the list of sets a, b, and c, state the domain of set b. domain of set b: {0, 6,5} domain of set b: {2, 4,-4, 0} set b does not have a domain

Which expression means three minus the product of two times a and five?