the general equation of a line is
where m is the slope and b the y-intercept
we can notice the y-intercept on the graph, is 12, because is the coordinate were x=0 or were the line touch the y-axis
now we need to find the slope, ussing
where (x2,y2) is a rigth point from (x1,y1), I can take any point of the line, for this case I will use (0,12) and (2,15)
where (2,15) is a right point from (0,12)
so, replacing
the slope is 3/2
now I can replace on the general equation ussing b=12 and m=3/2