first question is marked correctly ... use the Pythagorean theorem to answer the second question.
1. Since the system catches ±1%, you should write everything that in the range 7.29109 ± 1% = 7.29109 ± 0.0729109 = [7.21818 , 7.364].
You should thus add the third and last choice.
2. Maybe it is a "vector space" and the system wants to hear a+b and not the magnitude a^2+b^2. However, the way it is asked I agree your answer is right.