Adult tickets to the fall play cost $8 and student tickets cost $4. The drama class sold 30 more adult tickets than student tickets to the fall play. If the class collected $840 from ticket sales, how many adult tickets were sold?

Let a be the number of adult tickets sold, and s be the number of student tickets sold. We know that a = s + 30, and 8a + 4s = 840.

Substituting the first equation into the second equation, we get 8(s + 30) + 4s = 840
Multiplying through the parentheses, we get 8s + 240 + 4s = 840
Combining like terms, we get 12s + 240 = 840
Subtracting 240 from both sides, we get 12s = 600
Dividing both sides by 12, we get s = <<50=50>>50
Substituting this value back into the equation a = s + 30, we get a = 50 + 30 = <<50+30=80>>80. Answer: \boxed{80}.