The first thing to notice is that there is the variable k. Also, the right side of the equation includes a binomial (1+3k) in paranthesis multiplied by 6. In order to combine like terms and in turn, isolate the variable k, we have to use the distributive property. This means to multiply the outer "6" by each term in the binomial (1+3k). Remember PEMDAS (paranthesis, exponent, multiply or divide, add or subtract). So the first step looks like this:
-18-6k = 6*1 + 6*3k
The second step is multiplication (by order of operations PEMDAS). So then we have:
-18-6k = 6 +18k Notice that the 18 is defining how many "k's" there are.
Now comes the combining like terms part. Keep in mind we are isolating the variable. Basically, we want the "number and letter k buddies" like 18k and -6k to be on one side of the equal sign and the numbers without their "k" buddy on the other side (-18 and 6).
so here are the steps to do just that:
-18 -6k = 6+18k add 18 to both sides. You are doing the opposite operation to cancel out on the left.
-6k = 24 + 18k
-18k -18k subtract -18k. It cancels the 18k on the right.
combine the like terms -6k and -18k by subtracting the coefficient 18 from -6. This makes a bigger negative number.
-24k/-24 = 24/ -24 Lastly, we do the opposite function of dividing both sides by -24
k=-1 Yay we solved for k!