Are you asking about problem 3 or 5?
For #3, I would definitely use fractions rather than decimals; but your answer is correct. I would have written the work as [MATH]\frac{20}{3}\times 2 = \frac{40}{3} = 13\frac{1}{3}[/MATH].
For #5, I have no idea what you are thinking. Are you following some "magical" formula that you were taught, or thinking in some way I just can't see? Please explain.
In any case, your answer is wrong.
I would first find the segment above the "x", using the two similar triangles, and then find x by subtraction. I see several other more creative ways.