The amount he can spend for everything else is less than or equal to 1363
The inequality is :

Solution:
Let "s" represent the brother's money to spend
Your brother has $2000 saved for a vacation
His airplane ticket is $637
Write an expression for the total money spent by adding "s" and the price of plane ticket $ 637
We can frame a inequality as:

Here we have used "less than or equal to" symbol, because he can spent only up to 2000
Solve the inequality for "s"

Thus the amount he can spend for everything else is less than or equal to 1363