Hello!
Answer: 80 kilograms
Explanation: The sumo wrestler wanted to gain weight so an amount is being added to his current weight. As the question tells us, t is the months. Therefore 5.4 is the amount gained per month, resulting in 80 being the wrestler's starting weight. Whenever you are working on a problem like this just go through and figure out based on what you are told, what certain parts are, then go from there.
I hope that helps you!
Good luck!