Find the number of ways to pave a 1x5 rectangle by 1x1, 1x2, and 1x3 blocks, assuming that blocks of the same size are indistinguishable. O 20 O 18 O 16 O 14 QUESTION S The coefficient of ** in the expansion of (1 +x+x ) is O 882 O 686 O 1002 O 784