If you assume that the function of the form given, [tex]y= A/(x+ B)+ C, that contains 3 unknown parameters, A, B, and C. You need 3 equations to determine those three values. Rather than saying "there is not enough information", I would say "there is too much information"!
Put any three of those pairs of points into that formula to get three equations to solve for A, B, and C. If the function were, in fact, of that form, it wouldn't matter which of them you used- you would get the same thing.
For example, using just the first three pairs, x= 1.5, y= 56 gives 56= A/(1.5- B)+ C; x= 2, y= 20 gives 20= A/(2- B)+ C; x= 3, y= 10.2 gives 10.2= A/(3- B)+ C. Subtrating the second equation from the first eliminates C: 36= A/(1.5-B)- A/(2- B)= (2A- AB- (1.5A- AB))/((1.5-B)(2-B))= .5A/((1.5-B)(2-B)) or .5A= 36(1.5-B)(2-B). Subtracting the third equation from the first gives 47.8= A/(1.5-B)- A/(3-B)= (3A-AB- (1.5A- AB)/((1.5-B)(3-B))= 1.5A((1.5-B)(3- B)) or 1.5A= 47.8(1.5-B)(3-B). We can easily eliminate A from those two equations, leaving a quadratic equation in B.