Question 404651
Let x amount be at 6% then (4500 -x ) amount will be at 12%

so

(6/100)x + (12/100)(4500-x) = 315

6x + 12(4500-x) = 31500

6x + 54000 -12x = 31500

-6x = -22500

x = 3750

so 3750 amount was at 6% and 750 was given at 12% rate