You do 9x27=243 then take 2x31=62 add 243+62=305 then take 305 and subtract it from 28 305-28=277
so if i did it right you should get n=277
Dy/dx=1/2, 1/2, 1/2 etc
So this is a linear equation of the form y=mx+b where m=dy/dx=1/2 so
y=x/2 +b, now we can use any point to solve for the y-intercept, "b", I'll use (7,0)
0=7/2 +b
b=-7/2 so
y=x/2-7/2
y=(x-7)/2
25/6 converts to 4 1/6 so
4 1/6 x 2 = 8 1/3
8 1/3 is your answer :)