Start with
Multiply both sides by 3:
Recall that 21/5=4.2 to claim the correct answer.
It is one or it is infinite
In this type of questions, you just need to plug in the numbers you are given. But don't forget to put parentheses around negatives and use them wherever you want to clarify the equation.
Now let's take the exponents first:
Then do multiplications:
Then add plusses and minuses:
So the answer is -17.