Which expressions are differences of squares? select each correct answer

x^2+25
a^2-36
w^2-121
n^2-50

For this ones the second value is always negative so A is not correct. Also they have to have an exact square root which 50 doesn't. So the answers are B and C
(a-6)(a+6)
(w-11)(w+11)

Ac equals 35 cm long