Braniliest if right, provide steps,

she invested x amount at 10%, so 0.10x

she then invested 30,000 - x qt 7%, so 0.7(3-x)

they both earned 2400:

0.10x + 0.07(3-x) = 2400

now solve for x:

0.10x + 2100 - 0.07x = 2400

combine like terms:

0.03x + 2100 = 2400

subtract 2100 from both sides:

0.03x = 300

divide both sides by 0.03:

x = 300 / 0.03

x = 10,000

she invested $10,000 at 10% and $20,000 at 7%

both equations and proportions are better.