Your y= -x2 -10x +1 should be written as y = -x^2 -10x +1. This is a quadratic function. Because the coefficient (-1) of the x^2 term is negative, we know immediately that the graph (a parabola) opens down, and thus has a maximum.
Since line c and d are parallel, line a can act as a transversal. Thus, x=124 degrees because of the alternate exterior angle relationship that can be seen.
