Based on the given values above, in order for us to solve it, we need to make the units uniform first. So since the measurement of a rectangular water tank is in cm, we need to convert liters to centimeters cube. So 1 liter is 1000 cubic centimeter. This makes 576 liters 576,000 cubic centimeter. Now that we have the volume, let us recall the formula. V= lxwxh. Just simply plug in the values.
576,000 cm3 = l * 90cm * 40cm
576,000 = l * 3600cm2 (divide both sides by 3600cm2)
L = 160cm
Hope this answer helps.