At the beginning, the Jacuzzi is empty. So after 0 minutes there are 0 liters of water in the pool.

After 1 minute there are $1\cdot 40=401\backslash cdot40=40$ liters of water in the Jacuzzi.

After 2 minutes there are $2\cdot 40=802\backslash cdot40=80$ liters of water in the Jacuzzi.

After 5 minutes there are $5\cdot 40=2005\backslash cdot40=200$ liters in the Jacuzzi.

.......

and so on.

The completed table looks like this:

The plot looks as follows:

$xx$ : Time in minutes

$yy$: Amount of water in liters in the Jacuzzi

After $xx$ minutes we have $y=x\cdot 40y=x\; \backslash cdot40$ liters in the Jacuzzi.

So the function we are looking for is $f(x)=40\cdot xf(x)=40\backslash cdot\; x$

Adapting the function graph

Calculation of the time until the Jacuzzi is filled:

Insert the value $y=750y\; =\; 750$ in the function equation and solve for x.

So after about $1919$ minutes (precisely: 18 minutes and 45 seconds), the Jacuzzi is full.