Question

(2+6i)(2-6i)

Answer 1

You want to use FOIL.
F (first) 2*2
O (outside) 2*(-6i)
I (inside) 6i*2
L (last) 6i*(-6i)

then add together

Answer 2

Alternatively, you can jump to the identity that (a+b)*(a-b) is always equal to a^2+b^2