#### Explanation:

We shall first calculate the sales tax $\left(x\right)$ on the meal.

$x = 45 \times \frac{6}{100}$

$x = 9 \cancel{45} \times \frac{6}{20 \cancel{100}}$

$x = 9 \times \frac{3 \cancel{6}}{10 \cancel{20}}$

$x = \frac{27}{10}$

$x = 2.7$

The sales tax works out to $2.70. We now calculate the tip $\left(y\right)$on the pre-tax price of the meal. $y = 45 \times \frac{20}{100}$$y = 45 \times \frac{1 \cancel{20}}{5 \cancel{100}}$$y = \frac{45}{5}$$y = 9$The tip works out to $9.00.

The total cost of the meal is:

$45 + x + y = 45 + 2.7 + 9 = 56.70$