What formula generates the pairs (20,20), (40,40), (60,80), (80,160), (100,320)?

Hint - note that the y-value doubles for each increment in the x-value. This tells you that the formula is of the form 2^x, with appropriate scaling factors. Starting with this, can you now develop a formula that matches these points? Post back with your attempt and we'll help if you are still stuck.