Since you know that the equation of straight line is y=Mx + c
Where m mean gradient , and c means intercept
We don’t know our intercept neither do we know our gradient
So we have to find these to get our equation
Therefore, to find m( gradient) from the table
We are going to use the formulae for gradient which is
M=y2-y1 / x2-x1
I.e from the table
M= 23-15 / 4-2
M=8/2
M=4
Therefore how gradient is 4