First you would make the mixed fractions into improper fraction by multiplying the denominator and the whole number, then adding the numerator. Then you would flip the second fraction and multiply.
Ex. 1 1/2 ÷1 1/2
1st. 3/2÷3/2
2nd: 3/2×2/3
3rd 3/2x2/3=1
You said x + 2/5 = 12
It might be easier to handle if we use the decimal for 2/5.
x + 0.4 = 12
Subtract 0.4 from each side: x = 11.6
That's all there is to it. I'm sorry I can't make it
more complicated for you.
I believe that it is an example