an introduction to management science chapter3

I need help on #8,Chapter 3 for book "An introduction to management science 15th edition(Anderson, Williams)" Please help me...

The sensitivity report obtained through Excel solver is shown below: 6 Variable Cells Cell Name $B$24 Optimal Solution $B$25 U $B$26 H Final Reduced Objective Allowable Allowable Value Cost Coefficient Increase Decrease 0 0 0 0 1E+30 800037 0.5 12000 5 1 3.5 13 Constraints Cell Name $B$20 250 + 50H $B$21 0.50U +0.25H $B$22 U $B$9 Final Shadow Value Price 80000 0.093333333 700 1.333333333 800 0 0 Constraint Allowable Allowable R.H. Side Increase Decrease 80000 60000 15000 7 00 7 5 1000 1E+30 200 0 1E+30 0 300 Problem Refer to Figure 3.14, which shows the computer solution of Problem 7. a. How much would the return for U.S. Oil have to increase before it would be beneficial to increase the investment in this stock? b. How much would the return for Huber Steel have to decrease before it would be beneficial to reduce the investment in this stock? c. How much would the total annual return be reduced if the U.S. Oil maximum were reduced to 900 shares