The correct option is A is increased by 3
If each observation of the data is increased by 3, then their mean is increased by 3. Consider the following example:
Let the terms be a, b, c, d.
⇒Mean=a+b+c+d4After an increment of 3 in each term,⇒New mean=a+3+b+3+c+3+d+34 =a+b+c+d+124 =a+b+c+d4+3 =Mean+3
Hence, the mean also increased by 3.