Question 1032194
Where N is the number of monthly payments, i is the decimal interest rate per MONTH, A is the amount owed, and P is the payment amount.

N = -LOG(1-iA/P)/LOG(1+i)
i = 13.99% per year/100/12 months per year = .011658
A = $901.42
P = $20
N - -LOG(1-.011658*901.42/20) / LOG(1+.011658)
N = 64 months

Credit goes to http://brownmath.com/bsci/loan.htm#LoanNumber for the complete explanation and the basic formulas. I just had to figure out what they were using for i and put your numbers into it.