Can someone explain how to solve these? I have 10 questions I need to answer for problems like this & I can't go on until I solve it, so I just need the answer for this one and how to solve it. I need it finished fast because I need to bring up a low grade. Any help would be appreciated.

f(x) has value 150 at x= 0

and 0 at x= 3

so d(f(x))/dt = slope = -150/3 = -50

solve systems of equations by graphing. a system of linear equations contains two or more equations e.g. y=0.5x+2 and y=x-2. the solution of such a system is the ordered pair that is a solution to both equations. to solve a system of linear equations graphically we graph both equations in the same coordinate system