What is the 7th term in the sequence?

note: use the explicit rule.

an=30−4nan=30−4n

enter your answer in the box.
a7=a7=

Asap! i'm not good math and i'm lost.

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

How can you use synthetic substitution to tell whether a given binomial is a factor of a polynomial?