I'm pretty sure it's an infinite number of lines
If you're talking about PEMDAS it's Division. (Parenthesis., Exponents, Multiplication, Division, Subtraction just in case you forget)
7-4=3
10-7=3
13-10=3
we can see that this is an arithmetic sequence with a difference of 3
the nth term=the first term +(n-1) times the difference
so a(n)=4+3(n-1)