SOLUTION
Now Gina originally has $90 in her account. She takes $2 everyday
So since we are told to take d as the number of days, this means in any number of days, the amount she takes becomes

The amount left in her account should be gotten by subtracting 2d from the original amount of $90, so that becomes

Since we were told that a should represent the amount left, it implies that

Hence the equation for Gina's bank account is
