Step 1 :\(\text{Loan amount} = \text{Total cost of the house} - \text{Down payment}\)
Step 2 :\(\text{Loan amount} = \$320,000 - \$20,000 = \$300,000\)
Step 3 :\(\text{Monthly interest rate} = \frac{\text{Annual interest rate}}{12}\)
Step 4 :\(\text{Monthly interest rate} = \frac{48\%}{12} = 4\%\)
Step 5 :\(\text{Monthly interest rate} = \frac{4\%}{100} = 0.04\)
Step 6 :\(P = \frac{r*PV}{1 - (1 + r)^{-n}}\)
Step 7 :\(P = \frac{0.04 * \$300,000}{1 - (1 + 0.04)^{-180}}\)
Step 8 :\(P = \frac{\$12,000}{1 - (1.04)^{-180}}\)
Step 9 :\(P = \frac{\$12,000}{1 - 0.0184}\)
Step 10 :\(P = \frac{\$12,000}{0.9816}\)
Step 11 :\(\boxed{P = \$12,224.49}\)