卡西姆先生有一些芒果和苹果要出售。他卖了 144 个芒果。他卖出的水果中，有 40% 是苹果。

1. Find the percentage of sold fruits that were mangoes

Percentage of mangoes sold = $100\% - 40\% = 60\%$

2. Calculate the total number of fruits sold

$60\%$ of total sold = $144$
$1\%$ of total sold = $\frac{144}{60} = 2.4$
$100\%$ of total sold = $2.4 \times 100 = 240$

1. Find the total number of fruits Mr. Kassim had at first.

From part (a), the total number of fruits sold is $240$.
Since he sold $30\%$ of his fruits:
$30\% \rightarrow 240$
$1\% \rightarrow 240 \div 30 = 8$
$100\% \rightarrow 8 \times 100 = 800$
Total fruits at first = $800$

2. Find the number of apples left unsold.

Number of fruits left unsold = $800 - 240 = 560$
Percentage of unsold fruits that were apples = $100\% - 70\% = 30\%$
Apples left unsold = $30\% \times 560 = \frac{30}{100} \times 560 = 168$

3. Find the total number of apples at first.

Number of apples sold = $240 - 144 = 96$
Total apples at first = Apples sold + Apples left unsold
Total apples at first = $96 + 168 = 264$