18 = 10 + 2k
move 10 to the other side
sign changes from +10 to -10
18-10=10-10+2k
18-10= 2k
8= 2k
divide by 2 to get k by itself
8/2= 2k/2
Cross out 2 and 2 , divide by 2 and then becomes 1*1*k= k
k=8/2
Answer: k= 4
