If there are 150 total instruments in said Orchestra, we'll need to divide that number in half.
75, simple enough. Now we know that half of 150 is 75.
Start by writing your problem like this: 150= 75w+37.5b
That equation is all I can think of, because 37.5 is half of 75, which means that's roughly the number you're looking for. Sorry if this doesn't help much
