Let us assume that the number of men at the concert = M
The number of woman in the concert = W
In the given problem, it is already told that there are 3 times the number of men in the concert.
Then
W = 3M
M = W/3
Total number of men and women wearing glasses = 3M/5 + W/3
In the problem given, it is already told that there are 120 more women wearing glasses than men
Then,
3M/5 +120 = W/3
3M/5 + 120 = M
M - 3M/5 = 120
(5M -3M)/5 = 120
2M/5 = 120
M = 600/2
= 300
Number of Women in the concert = 3M
= 3 * 300
= 900
Then the total number of people in the concert = 300 + 900
= 1200