Answer:
$293.24
Explanation:
The amortization formula is good for this. (So are any number of financial calculators or apps.)
R = PV(r/n)/(1 -(1 +r/n)^(-nt))
for present value PV, annual interest rate r, term t in years, and n the number of compoundings per year.
R = $18,000(0.054/12)/(1 -(1 +0.054/12)^(-12·6)) ≈ $293.24
The periodic payment is $293.24.