$$ 5220 \div ? \times 15 = 2175$$

Let the unknown quantity be 'p'.

$$ 5220 \div p \times 15 = 2175$$

Taking 'p' on right hand side of equation and 2175 to left side of equation.

$$ 5220 \div 2175 \times 15 = p$$

Now,

$$5220=15\times348$$

$$2175=15\times145$$

$$5220 \div 2175 = \frac{15\times348}{15\times145}$$

$$5220 \div 2175=\frac{348}{145}$$

Hence,

$$ 5220 \div 2175 \times 15 = \frac{348}{145}\times15$$

$$145=5\times29$$

$$348=12\times29$$

Therefore,

$$ 5220 \div 2175 \times 15 = \frac{12\times29}{5\times29}\times15$$

$$ 5220 \div 2175 \times 15 = \frac{12}{5}\times15=36$$

So,

$$p=36$$

Hence, Option A is Correct.