Answer:
I will not give you an answer, but I will give you how too get the equation started.
Step-by-step explanation:
set up an equation using:
x= amount invested at 3%
7800 - x = amount invested at 12%
.03(x) + .12(7800 - x) = 504
.03x +936 - .12x = 504
-.09x = -432
x = 4800
