Well if you divide 7 divided by 12 you get 0.583 which you can round however you wish but I am not sure if that’s what you mean
        
             
        
        
        
PT = 15, and TB = 10 
Take the 15 from PT, and add the 10 from TB. Which equals 25. 
PB = 25 
So, 25 is your answer. 
Hope this helps! ☺
        
             
        
        
        
It helps to imagine the variable a sort of as a unit. Like with 5 minus 12 lemons, it has no bearings on the addition/subtraction here.
Factor out a and subtract.
