Which number is missing from the fact family? 4,6,10,16

Note that 6 is 4 plus 2, 
               10 is 6 plus 4, or 6 plus 2^2
                16 is 10 plus 6

Given the first term, 4, we find the second term by adding 2 to 4, obtaining 6.
Given the 2nd term, 6, we find the third term     by adding 4 to 6, obtaining 10.
Given the 3rd term, 10, we find the fourth term  by adding 6 to 10:  16
What's the next term?  Find the fifth term           by adding 8 to 16:  24 (answer)

The answer is $9.90 with rounding to the nearest tenth