20.8.
You multiply 5.2 times 4
Linear functions are those whose graph has a straight line.
The explicit formula for an arithmetic sequence is an = a1 + d(n - 1) where a1 is the first term and d = common difference. For this sequence a1 is 7 and d = 13- 7 = 19 - 13 = 25 - 19 = 6
So explicit formula required = 7 + 6(n - 1)