The given data is:
x 1 7 13 19
y 4 7 10 13
We can check there relationship whether it's linear or not by simply plotting the points on a scatter plot. From the attach scatter plot we can see that the it's linear relationship.
Next step is to find the slope of this data. Formula to find slope is,

Let's take the first two points (1,4) and (7,7). So, plug in x1=1, y1=4, x2=7 and y2=7 in the above formula. Hence,

=

=

Point slope form of a line is:

Now we can plug in m=1/2, x1=1 and y1=4 in the above equation. So,
.