6.2, 7.0
To find the common difference between two outputs you will subtract the current output number from the proceeding number. Ex 5.4 - 4.6 = 0.8 and 4.6 - 3.8 = 0.8. Because they are the same value it means the function increases at a rate of 0.8 for each input of a.
so 5.4 + 0.8 = 6.2
and 6.2 +0.8 = 7.0.