Question 1107792
0.10x + 0.12(10,000 - x) = 1080
0.10x + 1,200 - 0.12x = 1080
-0.02x = -120 divide, and remember that -/- = + so for the purpose of division you can ignore the negative sign
x = 6,000 
She invested 6,000 at 10% and 4,000 at 12%