i cannot understand where i am going wrong, the question is to find where the two curves

meet:

(squared=)

x+y=25 (1)

y=x-5 (2)

heres how i worked it out:

(1) y=25-x

y=5-x

subst y into 2

5-x=x-5

x+x-10=0

this does not factorise! help! i am mathematically challenegd and i work hard to try abd get good grades and things like this frustrate me, i can do all the other simluatneous eqns except this type