Focal length 20. Object 10, 30, 40, 50, 60.

$$\frac{1}{v} = \frac{1}{20} - \frac{1}{10}$$ $$\frac{1}{v} = \frac{1}{20} - \frac{2}{20}$$ $$\frac{1}{v} = -\frac{1}{20}$$ $$v = -20$$

$$\frac{1}{v} = \frac{1}{20} - \frac{1}{30}$$ $$\frac{1}{v} = \frac{3}{60} - \frac{2}{60}$$ $$\frac{1}{v} = \frac{1}{60}$$ $$v = 60$$

$$\frac{1}{v} = \frac{1}{20} - \frac{1}{40}$$ $$\frac{1}{v} = \frac{2}{40} - \frac{1}{40}$$ $$\frac{1}{v} = \frac{1}{40}$$ $$v = 40$$

$$\frac{1}{v} = \frac{1}{20} - \frac{1}{50}$$ $$\frac{1}{v} = \frac{5}{100} - \frac{2}{100}$$ $$\frac{1}{v} = \frac{3}{100}$$ $$v = \frac{100}{3} \approx 33.33$$

$$\frac{1}{v} = \frac{1}{20} - \frac{1}{60}$$ $$\frac{1}{v} = \frac{3}{60} - \frac{1}{60}$$ $$\frac{1}{v} = \frac{2}{60}$$ $$\frac{1}{v} = \frac{1}{30}$$ $$v = 30$$

Majibu ya umbali wa picha ($v$) kwa kila umbali wa kitu ($u$) ni:

• Wakati $u = 10$, $v = \boxed{-20}$
• Wakati $u = 30$, $v = \boxed{60}$
• Wakati $u = 40$, $v = \boxed{40}$
• Wakati $u = 50$, $v = \boxed{33.33}$
• Wakati $u = 60$, $v = \boxed{30}$