I believe that it should look like this:
if we say that the number we want to find is
, we will get:
<--- that's because diminish
means to substract. So the number we're looking for needs to be both divided by 6 (left side of the equation) and substracted with 40 (right side of the equation).
After that it's easier:
After that we can also check if the equation checks out too:
I hope it's right now ;)