The 'crab' means the 'sum of'
so the first one means the value of sum of 3 added together 20 - 3 = 17 times.
That is 3*17 = 51
The second one is the sum of the values of n^2 -2 when n = 1,2,3,4 and 5
= 1^2 - 2 + 2^2 - 2 + ....... + 5^2- 2
= 1 + 4 + 9 + 16 + 25 - 10
= 45
