The instructions state that Cheryl needs 4/9 square yards of one type of material and 2/3 square yards of another type of material for a project. She buys exactly that amount. After finishing the project, however, she has 8/18 square yards left that she did not use. What is the total amount of square yards of material Cheryl used?  Options:
A) 1 / 12  B) 1 / 9  C) 2 / 3  D) 1 1 / 9  E) 2 1 / 9

Rationale: "total bought = 4 / 9 + 2 / 3 left part 8 / 18 - - - > 4 / 9 so used part 4 / 9 + 2 / 3 - 4 / 9 = 2 / 3 answer : c"
Answer: C