The bar graph below shows the number of cars sold from January to March.

1. Read the number of cars sold in March from the bar graph

From the graph, the bar for March reaches a height of $9$.
Number of cars sold in March = $9$

2. Calculate the number of cars sold in April using the given fraction

Since March is $\frac{1}{4}$ of April:
$\frac{1}{4}$ of April = $9$
April = $9 \times 4 = 36$

1. Find the number of cars sold in April from part (a)

From part (a), March sold $9$ cars, which is $\frac{1}{4}$ of April.
Number of cars sold in April $= 9 \times 4 = 36$

2. Calculate the total number of cars sold from January to April

Total cars $= 30 \text{ (Jan)} + 18 \text{ (Feb)} + 9 \text{ (Mar)} + 36 \text{ (Apr)} = 93$

3. Calculate the average number of cars sold

Average $= \frac{\text{Total cars}}{\text{Number of months}} = \frac{93}{4} = 23.25$
Since the question asks for the average number of cars, we can leave it as $23.25$ or $23\frac{1}{4}$. (Note: Average can be a decimal even for discrete items).