When must a system of linear equations be solved algebraically, not graphically

Consider the function f(x)=-5x+3 what is f(-2)

Aprojectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = -16t2 + 704t. after how many seconds does the projectile take to reach its maximum height?

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.