y + 82 = 10x is the answer.
X and y are the numbers
y>x
sum (addition) of twice a number (2x) and larger number (y) is (=) 145
2x+y=145
difference between them is 55 (y is bigger so it would be x is subtracted from y)
y-x=55
so the equations are
2x+y=145 and
y-x=55
we could add x to both sides in the 2nd equation to obtain
y=x+55, but that doesn't really represent that the difference is 55, though they are the same euation
so I would say C and D only
Remember
difference of 2 perfect squares
a^2-b^2=(a-b)(a+b)
(x)^2-(7)^2=(x-7)(x+7)
set to zero
x-7=0
x=7
x+7=0
x=-7
x=-7 or 7