1. The answer should be 3.4. Since there are only 2 significant figures in the first number, your final answer should have at most only 2 significant figures, so adding 0.00344 to 3.4 will give you a value of 3.40344, but only the first two numbers count.
2. 14.9 is the answer. If you put it in your calculator you get a value of 14.85225, but the first number has 3 significant figures (the zero counts in this case) so you can have only 3 digits in your answer and the 8 gets rounded up to a 9.
3. 1.14 is the answer. Both numbers have 3 significant figures.
4. 153.4 is the answer. Both numbers have 4 significant figures.
5. 2700 is the answer. The second number has only 2 significant figures and when you put it into your calculator you get a value of 2671.24, but with only 2 significant figures this number becomes 2700 - after rounding.