Sean buys some T-shirts for $12 each and the same number of belts for $7.50 each. Write an expression in the simplest form that represents the total amount.
So n represents the same number for t-shirts and belts.
Therefore n x 12.50 + n x 7.50 OR n(12.50+7.50)
The problem the student made was that they multiplied 12 times n plus 7.50. They forgot to multiply n times 7.50.
An expression that represents the total amount spent is 12n + 7.50n
The question is somewhat confusing but assuming you mean where the submarine is after moving up 7 meters then down 38 meters the submarine would now be located 56 meters below sea level