Answer
a. See work below
b. Converging
c. 7.4 D
Work Step by Step
a. The problem describes a magnifying glass used in a way to obtain m= +3.0.
This is exactly the problem posed in example 23-13 on page 667. The ray diagram is precisely the same as the scaled diagram shown in Figure 23-43. The image is virtual, upright, and magnified.
b. Only a converging lens can make a virtual, upright magnified image. This will be confirmed by calculation; The lens should have a positive power.
c. $$m=-\frac{d_i}{d_o}$$
$$d_i=-md_o$$
Use the lens equation.
$$\frac{1}{d_o}+\frac{1}{d_i}=\frac{1}{f}$$
Solve for the power, 1/f.
$$P=\frac{d_o+d_i}{d_od_i}=\frac{d_o-md_o}{d_o(-md_o)}$$
$$=\frac{0.090m-3(0.090m)} {(0.090m)(-(3) 0.090m)}=7.4D$$