(a plus 7)(a plus 11)

Put (a plus 1) eq. x

x ^2 plus 16x  plus 6

x^2 plus 10x plus 6x

x(x plus 10) plus 6(x plus 10)

(x plus 10)(x plus 6)

(a plus 1 plus 10)(a plus 1 plus 6)

(a plus 11)(a plus 7).