Well, Subhotosh Khan gave you a "line of best fit" (which is actually a quadratic equation), although this doesn't pass exactly through any of the four points. You can easily create a quadratic (or cubic or any n-degree polynomial) that does pass exactly through all four points. But, as was also mentioned, there's no one unique equation by which you can derive the "original" function that created these points. Given the decimal nature of the values, creating a radical equation seems like a reasonable thing to do too. You said you "tried" to use a system of equations to solve it. You have four equations and four unknowns, so it's solvable (although "no solution" might be the answer). Where did you run into difficulties? Please share your work with us, even if you know it's wrong. Thank you.
