It’s 15 for #16 and then for #18 it would be 55 then for 20 it would be 6
First change the feet to inches. 80*12=960 Then set up a proportion 960/4=x/1.
You should get 240. I'm pretty sure this is right. :)
Y-5=-2(x-3)
The formula is y-y1=m(x-x1)
1. Find the slope
2. Replace y1 & x1 with the first point