b is the answer
given is a funciton
the table shows x values as 1,2,
f(x) values as 7,9,
since f(x) is linear there is a constant slope
this shows that for a unit change in x, there is a 2 increase in f(x)
by this property, we get when 6 increases to 7, 17 will change to 19
i.e. 2 will be added to 17 to get next table value.