this time i want a better answer and explenation.
3k - 1 = 7+2 ..... simplify the right side
3k -1 = 9 now....add 1 to both sides so that we can have just 3k on the left side
+1 +1
3k = 10 divide both sides by 3
k = 10 / 3 and that's it !!!