1400 invested in two mutual funds one earned 6% profit the other earned 4% profit total profit 80. how much invested in each account

P=1400
I=80
Assume t=1 
 
or... 

 
for convenience we multiply by 50 

 

and the total principal is: 


 
then we double each term 

 



Next we subtract to solve 


 

 

and thus 
 



:)