Question 860175
Plot the points!  The curve could be lots of things.  The arrangement seen on paper may suggest a cubic function, with negative leading coefficient, and maybe an inflection point between the x=3 and x=5 values.


With those ideas, start with {{{y=ax^3+bx^2+cx+d}}}.
The four points will give you four equations, and the unknown, a, b, c, and d, are a count of four; so you will have a system of four equations to solve for a, b, c, and d.