Excel - Trend Formula

Hi,

I require a formula in the attached spreadsheet to fill in the blank numbers.

The spreadsheet contains numbers from 0 to 135 with values entered in increments of 15. I now want to see if there is a formula that can be used to work out the other values (which would produce a tangential curved line rather than a straight line if entered into a chart).

The values I have entered are for example only. They have no meaning and the formula would need to be such that I can easily change those numbers and the numbers around them would also change to suit.

0 = 0

15 = 0.24

30 = 1.28

45 = 1.93

60 = 2.34

75 = 2.89

90 = 3.01

105 = 3.93

120 = 4.75

135 = 5.21

ie. what would 97 equal?

ie. if I changed 105 to 3.84, the value for 97 would also change.

I hope that makes sense. Please let me know if there are any questions.