lamarco's Problem

I went to the mall with 124.3 dollars and i left with 30.1 dollars.How much did i spend at the mall?
first you draw a number line, the you put the 30.1 from 124.3 going subtracting.then jumps three times backwards then 1 tenths.The answer is 94.2 i got that answer by subtracting 124.3-30.1