First Step: We are simplifying the left-hand side by multiplying the coefficient to the (2x + 9)
Second Step: We subtract 30x from both sides to get all the x's on one side
Third Step: We add (or subtract in this case) like terms, which in this case you're taking 30x from 150x
Fourth Step: You subtract the remaining constant (675) from both sides to isolate your variable (x) on one side
Fifth and Final Step: You divide both sides by x's coefficient, 120, to get the value of x by its self