5. Class 7887 has 2:7 math classes daily. How many math classes do they have
after 21 days?

The equation x2 – 1x – 90 = 0 has solutions {a, b}. what is a + b?

Can some one me with these questions

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