An excited hydrogen atom emits light with a frequency of 1.141 multiplied by 1014 Hz to reach the energy level for which n = 4. In what principal quantum level did the electron begin?
Balmer's formula: $\displaystyle \frac{1}{\lambda} = R \left(\frac{1}{n_{f}^2} - \frac{1}{n_{i}^2}\right)$
You have $\displaystyle \frac{1}{\lambda}$ (can figure out the frequency), R (the Rydberg constant), and $\displaystyle n_{f}$ the final energy level of the electron.
Just a matter of algebra from here to solve for $\displaystyle n_{i}$.