QUESTIONS 9 AND 10 REQUIRE WRITTEN SOLUTIONS WHICH MAY INCLUDE PROOFS....

3. A selection of 3 whatsits, 7 doovers and 1 thingy cost a total of $329. A selection of 4 whatsits, 10 doovers and 1thingy cost a total of $441. What is the total cost, in dollars, of 1 whatsit, 1 doover and 1 thingy? [3 marks]