A 95% confidence interval on the z-table is 1.96.
Now find the standard error using the formula: standard deviation / square root sample size:
0.7 / √100 = 0.07
Multiply to the confidence interval: 1.96 x 0.07 = 0.137 = 0.14
Now add and subtract tot he average weight:
14 - 0.14 = 13.86
14 + 0.14 = 14.14
The answer is 13.96 ≤ u ≤ 14.14