Slope would be m=6/11 line would be 
Y=6/11x+255/11
So to find the slope, you would use the points given and the formula 
X2-X1/Y2-Y1
(18,33) and (42,77)
 X1,Y1            X2,Y2
So fill in the numbers 
42-18/77-33 
simplify 
24/44=6/11
So slope would be m=6/11
 Then to continue to find out how to graph it you would use the formula 
Y-Y1=m(X-X1)
Y-33=6/11(x-18)  
multiply the right side parentheses 
Y-33=6/11x-108/11
Then add 33 to the right side 
Y=6/11x+255/11