Answer:
 25 months
Step-by-step explanation:
We can use the amortization formula to solve for t.
That formula tells you the monthly payment as a function of interest rate (r=.14), compounding periods per year (n=12), principal borrowed (P=4200), and number of years (t). Using the given values, we have ...
 200 = 4200(r/n)/(1 -(1 +r/n)^(-nt))
 1 -(1 +r/n)^(-nt) = 4200(r/n)/200
 1 -21r/n = (1 +r/n)^(-nt)
 log(1 -21r/n) = -nt·log(1 +r/n)
 -log(1 -21r/n)/log(1 +r/n) = nt . . . . . . the number of months we want
 -log(1 -21(0.14)/12)/log(1 +0.14/12) = nt = 24.23
It will take Daisy about 25 months to pay of her credit card.
