What temperature is 15 degrees lower than 7 degrees celsius

The system of equations graphed below has how many solutions?

Find the vertex for the parabola given by the function ƒ(x) = −3x2 − 6x.

The perimeter of △cde is 55 cm. a rhombus dmfn is inscribed in this triangle so that vertices m, f, and n lie on the sides cd , ce , and de respectively. find cd and de if cf=8 cm and ef=12 cm. the answer is not cd=20 and de=15. i have tried that one, it does not work.