Answer:

» Collect like terms, r terms on the left hand side by subtracting r from both sides and adding st to both sides

» On the left hand side, factorise out r

Answer: - x - 120
Explanation: You want to find the opposite of (120-x) not just x, so you just put the negative symbol next to both the variables.
1.3005 x 10^4
10 to the fourth power