Suppose nick spent x number of tokens on day 1
So he spent x + 5 on day 2
He spent x + 10 on day 3
He spent x + 15 on day 4
He spent x + 20 on day 5
On day 6 he spent x + 25
And on day 7 he spent x + 30
So in all he spent
x + x + 5 + x + 10 + x + 15 + x + 20 + x + 25 + x + 30
= 7x + 105
But total token spent = 203
So
7x + 105 = 203
Subtracting 105 from both sides
7x = 203 - 105
7x = 98
Dividing by 7 on both sides
x = 14
So on third day he spent x + 10
= 14 + 10
= 24 tokens
Tokens spent on day 3 = 24