here we have graph which is the shape of parabola and a staright passing through y .
we know that general equal of parabola lies x axis
y=x^2
and the equation of straight line y=5
it means y=mx+b
where it is a straight line it does not have slope so m=0 x intercept is also 0 and y intercept is 5 .
if we plug these equation in straight line equation we get y=5