You need to rearrange to isolate the variable t.
Starting with the formula
A = P (1+r/n)^{nt}
Isolate term with unknown exponent
A/P = (1+r/n)^{nt}
It might be useful to plug the values in, at this step, to simplify the work.
(1700+500)/1700 = (1 + .07/4)^{4t}
1.29412 = (1.0175)^{4t}
Rearrange a little, to simplify, a little more, moving the constant part of the exponent into the parentheses
1.29412 = (1.0175^{4})^{t}
Evaluate the statement in parentheses
1.29412 = (1.07186)^{t}
Take log of both sides to eliminate the exponent.
log 1.29412 = log 1.07186^{t}
Use power property of exponents
log 1.29412 = t * log 1.07186
Isolate the variable
t = log 1.29412/log 1.07186
Evaluate, then round to appropriate figures.
5/14/2014

Regina G.