Hello!
First, set a variable for "spending $2 each day". This is important as the number of days passed is not set, and it varies, so we need a variable for it. Say d = number of days passed.
Now, write out the equation. The first thing we want to write is "You had $150". This can be represented by just writing out the number 150.
Our equation now: 150
Finally, add the variable. This would be "you are spending $2 each day". For this, you must subtract 2 times d from 150.
Our final equation: 150 - 2d
Hope this helps!
