Step-by-step explanation:
x = the first number of the sequence
x + (x+1) + (x+2) + (x+3) + (x+4) + (x+5) = 519
6x + 1 + 2 + 3 + 4 + 5 = 519
6x = 504
x = 84
so, the third number is x+2 = 84 + 2 = 86
