7y = 14x and y = 2x does have infinitely many solutions. Why? Because the first equation can be rearranged to look like the second one. If you divide 7y and 14x by 7, you end up with y = 2x. Look familiar? This means the set of equations has infinitely many solutions.
The probability of selecting a black or blue pen is 4 out of 13. You calculate this by adding the amount of pens together and comparing it to the total amount of pens and pencils in the cup.
