Hi there! I'll walk you through.
First, when you multiply a decimal by a 10, 100, 1000, etc. you need to move the decimal n spaces to the right, where n is how many 0's are in the multiple.
So, 1.47 * 10 = 14.7
Remember PEMDAS. Now we need to do the other side.
3.56 * 10 = 35.6
Now, subtract!
14.7 - 35.6 = -20.9
And there you are. :)