There are

ways of selecting two of the six blocks at random. The probability that one of them contains an error is

So

has probability mass function

These are the only two cases since there is only one error known to exist in the code; any two blocks of code chosen at random must either contain the error or not.
The expected value of finding an error is then
Emma’s age is 26 and her sister is 15 because 26 - 15 = 11 (The age that Emma is older by) and once you add 26 and 15, it equals 41
The formula for the area of a parallelogram is base times height or bh.
There's a formula sheet on Khan Academy:
https://www.khanacademy.org/math/basic-geo/basic-geo-area-and-perimeter/parallelogram-area/a/area-of...