Please help in confused

Which expressions are equivalent to k/2 choose 2 answers: a k-2 b 2/k c 1/2k d k/2 e k+k

How many 3-digit numbers can you write using only digits 1 and 7? (of course, digits can repeat.) how many 3-digit numbers can you write using only digits 1 and 7? (of course, digits can repeat.)

Use the distributive property -7(-2x+u-2)