Question

Cary and her friends Tasha both had 20 tickets each to play games. Cary used x of hers and Tasha used 2 times as many as Cary. When Cary's dad doubled the combined amount they had left, they ended up with 39 tickets. How many tickets(x) did Cary use?

Answer 1

Cara   had (20-x) tickets that left.
Tasha had (20-2x) tickets that left.

Tasha and Cara together
(20-x) +(20-2x)=20+20-x-2x=40-3x 

Tasha and Cara together had  (40-3x)  tickets that left.

Dad doubled it    
2*(40-3x)

Now they have
(40-3x) +2*(40-3x)=39

40-3x+80-6x=39
120-9x=39
9x=120-39
9x=81
x=9

Cary used 9 tickets.