It's very simple, it's just multiplication but with fractions. You can work this out with one of two ways:
Using decimals
Using decimals is the same thing as normal multiplication, but you move the decimal the number of digits to the right of the decimal. For example, 125678 x 56 equals 7037968, but with the decimal, 1256.78 x 56 = 70379.68
You move the decimal to places to the right because there are two numbers to the right of the decimal in the number that has the decimal, or 1256.78.
Using fractions
You can convert the decimal to a fraction and multiply from there, but in this case, it is easier to leave it as a decimal. However, 1256.78 as a fraction would be 1256 78/100