When concentrations of formaldehyde in the air exceed 33 mu g divided by ft cubedg/ft3left parenthesis 1 mu g equals 1 microgram equals 10 Superscript negative 6 Baseline gram right parenthesis comma(1g=1microgram=106gram),a strong odor and irritation to the eyes often occurs. A room having floor dimensions of 10 ft by 10 ft and height of 77ft uses the equation

Upper F equals 117 comma 775 xF=117,775x

to model the amount of formaldehyde F in the room after x days. How long will it take before aperson's eyes become irritated in theroom?