Javier asks his mother how old a tree in their yard is. His mother says, “The sum of 10 and two-thirds of that tree’s age, in years, is equal to 50.” Javier writes the equation (10 + two-thirds) a = 50, where a is the tree’s age in years. His equation is not correct. What error did he make? The variable a should be multiplied by 10 only, and then added to Two-thirds. The variable a should be multiplied by Two-thirds only and then added to 10. The variable a should be multiplied by 50, not by the sum of 10 and Two-thirds. The variable a should be multiplied by Two-thirds and 50 and set equal to 10.