What are the solutions to problems 16-20?

$$3x + 5 - 5 = 23 - 5$$ $$3x = 18$$

$$x = \frac{18}{3}$$ $$x = 6$$

The solution is $\boxed{\text{6}}$.

17. It is a quarter to 9 o'clock. Draw a clock face to show this time.

"A quarter to 9 o'clock" means 15 minutes before 9 o'clock, which is 8:45.

• The minute hand points to the 9.
• The hour hand is between the 8 and the 9, closer to the 9.

18. Simplify: $4x + 5y + 2x - 3y$.

$$6x + 2y$$

The simplified expression is $\boxed{6x + 2y}$.

19. How many quarter litre bottles can be obtained from 7 litres of water?

$$\text{Number of bottles} = \frac{\text{Total volume}}{\text{Volume per bottle}}$$ $$\text{Number of bottles} = \frac{7 \text{ litres}}{\frac{1}{4} \text{ litre/bottle}}$$

$$\text{Number of bottles} = 7 \times 4$$ $$\text{Number of bottles} = 28$$

You can obtain $\boxed{28}$ quarter litre bottles.

20. Calculate the length of the rectangle below whose area is $42 \text{dm}^2$.

The area of a rectangle is given by the formula: Area = Length $\times$ Width.
Given: Area $= 42 \text{ dm}^2$, Width $= 6 \text{ dm}$, Length $= L$.

$$L = \frac{42 \text{ dm}^2}{6 \text{ dm}}$$ $$L = 7 \text{ dm}$$

The length of the rectangle is $\boxed{7 \text{ dm}}$.