Try this:
A = [...
745 780 800 860 810
780 780 760 695 815
744 825 720 690 750
715 860 700 670 620]
B = [...
30 18 40 58 26
70 19 72 29 47
14 48 40 14 48
13 72 59 66 72]
% N = input('Type a number : ')
N = 745;
% Count how many are below the threshold.
mask = A < N
sumBelowThreshold = nnz(mask)
% Get the values at the same locations in B.
% First as a list:
valuesBelowThreshold = B(mask)
% Then as a masked array
Bmasked = B .* mask
You'll see in the command window:
sumBelowThreshold =
8
valuesBelowThreshold =
14
13
40
59
29
14
66
72
Bmasked =
0 0 0 0 0
0 0 0 29 0
14 0 40 14 0
13 0 59 66 72
