The total number of marbles in the box is:
$10 + 30 + 20 + 15 = 75$
The probability of drawing a red marble first is:
$\frac{10}{75}$
Since replacement is made, the probability of drawing a white marble next is:
$\frac{30}{75}$
Therefore, the combined probability of first drawing a red marble and then a white marble is:
$\frac{10}{75} \times \frac{30}{75} = \frac{4}{75}$