In this problem, we calculate the operating voltage of the flashlight battery, since we know the current and power, we use the following relation:

$$
P = UI
$$

Expressing the voltage we have:

$$
U = frac{P}{I}
$$

Putting in the information from the problem statement we have:

$$
U = frac{4.5 mathrm{W}}{3 mathrm{A}}
$$

we get the result of:

$$
boxed{color{#c34632}U=1.5 mathrm{V}}
$$

$$
U=1.5 mathrm{V}
$$

Here we calculate the power produced by a small battery that is a starter for a gasoline engine. Since we know the current and voltage, we use the following relation:

$$
P = UI
$$

Putting in the numbers we have:

$$
P = 12 mathrm{V} cdot 0.75 mathrm{A}
$$

which gives the result of:

$$
boxed{color{#c34632}P = 9 mathrm{W}}
$$

$$
P = 9 mathrm{W}
$$