Given vector a = (3,1), vector b = (1,3), vector C = (k, 7), if (vector a-vector C) is parallel to vector B, then what is k equal to

Given vector a = (3,1), vector b = (1,3), vector C = (k, 7), if (vector a-vector C) is parallel to vector B, then what is k equal to

a-c = (3-k,-6)
a-c// b
=> -6/(3-k) = 3/1
-6 = 9 -3k
k = 5