APV and WACC

Hello, sir!

A question about APV. We usually use the NPV if all equity finance + tax shield technique.
Could we use the MM formula and WACC to get the APV?

For example:
A project costing $100,000 is to be finance by $60,000 of irredeemable 12% loan stock and $40,000 of new equity. The project will yield an after-tax annual cash flow of $21,000 in perpetuity. If it were all equity financed, an appropriate cost of capital would be 15%. The tax rate is 30%. What is the project`s APV?

My calculations are:

Ke = 15% + (1-30%)*(15%-12%)60/40 = 18,15%

WACC = 40/100*18,15% + 60/100*12%*0,7 = 12,3%

APV = $21000/12,3% – $100000 = $70 731.

Wich does not equal to the correct answer, using the NPV if all equity finance + tax shield technique:
NPV if all equity finance = $21,000/0,15-100000 = 40,000
PV of tax shield = $60,000*12%*30%/0,12 = 18,000
APV = 58,000

Thank you in advance!