Systems of linear equations - no solution, unique solution, infinite solutions

I'm just gona copy these from my book:

1. x-y = 6 and 2x-2y = 12 have infinitely solutions, show this using parameters?

Obviously both equations are the same line, but the answer is x = t+6 where t = real number

I assume a 3rd variable is involved...

2. Find the values of b and c for which equations x+5y = 4 and 2x + by = c that have

a. a unique solution b. infinite set of solutions c. no solution

3. Solve simultaneous equations 2x-3y = 4 and x + ky = 2 where k is a constant, also, find value of k with no unique solution

How do I solve these (Worried)