Question

I need to know the answer

Answer 1

The right side has the apex of the roof on it, point (5,5).  From the picture we see its slope is -1.  It has to be the negation of the left slope for a symmetrical roof.

Point slope form tells us

y - b = m (x - a)

y - 5 = -1 (x - 5)

y = -x +5 + 5

y = -x + 10

Answer: y = -x + 10