Problem #$3$: In a mixing vat there are initially $300$ litres of volatile liquid. $3$ litres of fresh liquid are added per hour, but $15\%$

of the current content of the vat is lost each hour due to evaporation. How many litres of liquid are there after $4$

hours?

$[$:

Enter your answer symbolically,

as in these examples

Problem #$3$: $\frac{{258}^4}{{300}^3}$