Hi, You had the right idea..
7a^2 + 53a + 28 |note the use of the ^2 for 'squared'
(7a + _)(a + _)
What 2 numbers have a 'product of 28' that would work in the blanks?
such that the SUM of the inner product and the outer product = 53a
(7a + 4)(a + 7)
SUM of the inner product(4a) and the outer product(49a) = 53a
7a(a + 7) + 4(a + 7) = 7a^2 + 49a + 4a + 28 = 7a^2 + 53a + 28