(x-7)(x+6)> 0 solve non linear inequality

:24% of students in a class are girls. if there are less than 30 students in this class, how many students are there? how many girls are there?

Last one and the bottom answer choice is y=(x-4)^2+1 you guys!

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters