Step by step solution: I started by making an equation in slope intercept form- I found the slope, 28/17, with the points (4, 17) and (12.5, 31). Then I found the y intercept, 1, with the point (4, 17). So the equation is y=28/17x+1. Then I just plugged 18.5 where the x is and solved for y
28/17(18.5)+1=y 28/17(37/2)+1=y 1036/34+1= y 30.47+1=y y=31.47
Keep in mind that 1036/34 is not exactly 30.47 but that 30.47 was rounded to the nearest hundredth