Find a quadratic equation for a function 𝑦=𝑓(𝑥)) which crosses the x-axis at 𝑥=−3] and 𝑥=6, and which crosses the y-axis

We  have  this

y =  a ( x + 3)  ( x - 6)

And  the point   (0, -72)  is on the  grpah....so we  can  find  "a"  as

-72  =  a  ( 0 + 3)  ( 0 - 6)

-72  =  a  ( 3) ( -6)

-72  = -18a

-72  /-18  =  a  =    4

f(x)  =

4 ( x + 3) ( x - 6)

4 ( x^2  - 3x - 18)

4x^2  - 12x  - 72