Pls help solve
10th grade mathematics

Solve for x -2.3(r - 1.2 ) = -9.66 enter you answer as decimal.

0if x and y vary inversely and y=6 as x=7, what is the constant of variation?

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