Since you are supposed to decrease the number in the ratio 3:8 or 3/8 you take the small number that is 3 to be the numerator and 8 to be the denominator then multiply it by 18.4.
That is 18.4×3:8= 184/10×3/8=6.9
So to decrease a number you multiply it with the smallest number as the numerator and the big number as the denominator
To increase a number you multiply it with the big number as the numerator and the small number to be the denominator
