I need some help on 2 questions please?

1. Which trinomials are perfect square trinomials?

Select all correct answers.

a^2+15a+75

a^2+14a+49

a^2+4a+16

a^2+26a+169

2. Which expressions are differences of squares?

a^2-36

x^2+25

n^2-50

w^2-121