An annual salary of K31 600 had an increase of 8%. What is the new annual salary?

$$\text{Increase} = 8\% \text{ of K}31600$$ $$\text{Increase} = \frac{8}{100} \times 31600$$ $$\text{Increase} = 0.08 \times 31600 = \text{K}2528$$

$$\text{New Salary} = \text{Original Salary} + \text{Increase}$$ $$\text{New Salary} = \text{K}31600 + \text{K}2528$$ $$\text{New Salary} = \text{K}34128$$ $$\boxed{\text{K}34128}$$

6. An item sold at K25 is now marked at K17. What is the percentage decrease?

$$\text{Decrease Amount} = \text{Original Price} - \text{New Price}$$ $$\text{Decrease Amount} = \text{K}25 - \text{K}17 = \text{K}8$$

$\frac{\text{Decrease Amount}}{\text{Original Price}} \times 100\%$.

$$\text{Percentage Decrease} = \frac{8}{25} \times 100\%$$ $$\text{Percentage Decrease} = 0.32 \times 100\% = 32\%$$ $$\boxed{32\%}$$

7. Winel bought twenty bags at K18 and decided to sell them at K25 each. What is Winel's total profit?

$$\text{Total Cost} = \text{Number of Bags} \times \text{Cost per Bag}$$ $$\text{Total Cost} = 20 \times \text{K}18 = \text{K}360$$

$$\text{Total Revenue} = \text{Number of Bags} \times \text{Selling Price per Bag}$$ $$\text{Total Revenue} = 20 \times \text{K}25 = \text{K}500$$

$$\text{Total Profit} = \text{Total Revenue} - \text{Total Cost}$$ $$\text{Total Profit} = \text{K}500 - \text{K}360 = \text{K}140$$ $$\boxed{\text{K}140}$$