In the equation, it states "3.59p represents the cost of the corn for a number of packages", well we already know that 3.59 is the price, so the only part of that sentence left is the number of packages.
You first must distribute the negative sign to 3x+7, giving you -3x+7. Then you combine like terms (the 9x+(-3x) and 10+(-7)). This would give you 6x+3
