<PRE><B>Question 297541</B>
First, find the slope using the points. Slope (M) = y2-y1/x2-x1

(2,113) (5,209)

M = (209-113)/(5-2) 
  = 96/3
  = 32

Now pick a point, say (2,113).  Plug in the x,y and m values in the equation and solve for b

113 = 32(2) + b
113 = 64 + b
113-64 = 64-64+b
49 = b

Your equation is C = 32n + 49

The cost for 4 days...just plug in 4 for n. Multiply 4 times 32 and add that to 49

 C = 32(4)+49
 C = 177</PRE>