hi everyone, ive been having trouble with this word problem for the past while and I was wondering if i could get some help

The question is: Let f(x) = x^2 - nx + 5 and g(x) = mx^2 + x -3. The functions are combined to form the new function h(x) = f(x) + g(x). Points (1,3) and (-2,18) satisfy the new function. Determine the values of m and n.

if anyone can solve the equation and explain briefly what you did moving from step to step i would be grateful

thanks