Let S= the amount of money Sarah has.
Let J= the amount of money Jose has
J= S+20
J+S=90
But we also know that J can equal S+20
So,
S+20+S=90
2S+20=90
2S=70
S=35
So Sarah has $35, and Jose has $35+$20, so he has 55$
The answer would be 3.3944867e+29 but seeing how you didn’t give more detailing I’m not sure if it’s specifically the answer you need.
We know that the number of users triple each day
Let number of users on day 1 be x
⇒ Users on day 2 =
= 3x
and Users on day 3 =
= 9x
And so on...
% Increase in users from day 1 to day 2 = 
⇒ % Increase in users from day 1 to day 2 = 
⇒ % Increase in users from day 1 to day 2 = 
⇒ % Increase in users from day 1 to day 2 = 200%
Similarly,
% Increase in users from day 2 to day 3 = 
⇒ % Increase in users from day 2 to day 3 = 
⇒ % Increase in users from day 2 to day 3 = 
⇒ % Increase in users from day 2 to day 3 = 200%
Hence, we can see that the percentage increase each day is 200%