$$P={R * CCB \over 1-(1+R)^{-t}}$$ P stands for monthly payment, R is the interest rate,CCB is the initial credit card balance,t is the number of months until the debt is paid.
I would like to derive the formula for t ! $$-(1+R)^{-t}={R*ccb \over P} -1$$ After this How should I proceed !
multiplying by the denominator and dividing by $P$ gives$$1-\frac{R\cdot CCB}{P}=(1+R)^{-t}$$ taking the logarithm on both sides we get $$\ln\left(1-\frac{R\cdot CCB}{P}\right)=-t\cdot (\ln(1+R))$$ so we find $$-\frac{\ln\left(1-\frac{R\cdot CCB}{P}\right)}{\ln(1+R)}=t$$