The first step for solving this is to distribute 5 through the parenthesis.
5b + 30 = 18
Now move the constant to the right side of the equation and change its sign.
5b = 18 - 30
Calculate the difference between the two numbers on the right side of the equation.
5b = -12
Lastly,, you need to divide both sides of the equation by 5.
b = -
You can convert this fraction into a decimal by dividing the top of the fraction by the bottom. When you do this you should get -2.4 which will make the correct answer to your question option B.
Let me know if you have any further questions
:)