Solution
0.14x + 0.08(10000 - x) = 1220 Remove the brackets.
0.14x + 800 - 0.08x = 1220 Combine like terms on the left
0.14x - 0.08x + 800 = 1220
0.06x = 1220 - 800 Subtract 800 from both sides
0.06x = 420 Divide by 0.06
x = 420 / 0.06
x = 7000 Answer