Answer:
Bobby has 45 beads
Explanation:
Let x be the number of beads Bobby has.
Then, (x + 30) is the number of beads Alvin has.
Then, 3 (x + 30) is the number of beads Cathy has.
3 (x + 30) + (x + 30) + x = 345
3x + 90 + x + 30 + x = 345
5x + 120 = 345
5x = 225
x = 45
Therefore, Bobby has 45 beads.