Hi Mia,
Assuming that your measurements are the length, width and height of a box, the formula for volume is
V = L x W x H
So all you have to do is multiply 0.5 and 1.5, remembering that you'll have to move the decimal point in your answer 2 places to the left since each of the two numbers that you have multiplied have decimals one place to the left.
Then take your answer and multiply it by 0.4, remembering to move the decimal point in your answer 3 places to the left.
Have fun.
Dan