book Maths Puzzle Numerical Ability

Solve by completing the square:
3x(x being squared) + 4x = 4

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book Other Question

Find the eccentricity of the ellipse given by 16x^2 + 25y^2=100 A man invests $10,000 for a year. He lost twice what he gained. He ends with $8,000.
What is gained?
What is lost?

I didn't do algebra in school, so I don't know formulas.