Answer: d=6.
Explanation:
Let's write the condition of the problem:
a₁=7 a₆=37 d=?
The formula for the nth member of an arithmetic progression is:

Hence,
a₆=a₁+(6-1)*d
37=7+5*d
37-7=7+5*d-7
30=5*d
Divide the left and right sides of the equation by 5:
6=d
So, d=6.