Question 760657
let 'a' be the quantity of items purchased.
let 'b' be the original cost of each item.

(a)(b) = 4000  This is Equation 1

(a)(b + 50) = 5000 This is Equation 2

Solve Equation 1 and Equation 2 simultaneously.  
Step 1: Solve for 'a' in Equation 1 to get (a)=4000/(b)

Step 2: Substitute 'a' from step 1 for 'a' in step 2 to get Equation 3 below

(4000 / b)(b + 50) = 5000 This is Equation 3

Step 3: Solve Equation 3 for 'b' to get b=$200

'b' is the original cost of each item.  Therefore the answer is $200.