Your radiologist asks you to repeat a scan in order to doubl…

Your radiologist asks you to repeat a scan in order to double your SNR. The parameters are T1-weighted SE with a 500 ms TR, 20 ms TE, 1 NEX, 256 x 256 image matrix.  What parameter will you change in order to double SNR and what do you change it to?  What will the resultant scan time be for this scan assuming all other parameters are unchanged?