Solve the Problem $L$ Of an Optical Telescope with Lens Diameter $D$

Solve the problem.
-The limiting magnitude $L$ of an optical telescope with lens diameter $D$ (in inches) is given by $L ( D ) =$ $8.8 + 5.1 \log D$ .
a. Find the limiting magnitude for a telescope with a lens 11 in. in diameter. Round to 1 decimal
b. Find the lens diameter of a telescope whose limiting magnitude is 10.7. Round to the nearest $\mathrm { i }$

A) a. $14.1$
B) a. $5.3$
C) a. $2.4$
D) a. 21
b. $2 \mathrm { in }$ .
b. 2 in.
b. 14 in.
b. 1 in. .