The sum of normally distributed variables is also normal.
Work out the mean and standard deviation of and use those as the paramters for the distribution of the wall.
Hint: for independant variables
Once you have found the distribution of y
You want P(y>204) + P(y<196)
If you dont remember how to do that, you need to standardise the normal variable.
Ill do the first one:
The expression in brackets is jus a number, you can look it up in your standard normal table.
You should be able to do p(y<196) from that method or by general reasoning. If you are totally stuck you can read the spoiler below