[填空题]
As early morning passed toward midday, and the sunlightz2d k-e9nae l2l ww/ j(mx5cd5 got mp6d urn- 9 xvam1 mmpf+8zu:m9ore intense, a photographer noted that, if she kept her shutter mu9 p86 dm1p+u9 xfraz:-vmnm speed constant, she had to change the $f$-number from $f/5.6$ to $f/22$. By what factor had the sunlight intensity increased during that time? $I_2$ = $I_1$
