Answer:
135kg
Explanation:
In room number one, there are five old models and a new model, which weights 240kg. So, it can be concluded that there are 6 models in there, and we can write it as 5x ( x = old models ) + 240 ( weight of new model ). then informed room number two, there are 3 old models and a new one, weighting 510kg. write it as 3x + 510.
the equation will be as: 5x + 240 = 3x + 510
move 3x to the front behind 5x, move +240 to the back behind 510. you will get 5x - 3x = 510 -240
which will be 2x = 270, then move 2 behind 270, means 270 divide 2, which then you will get 135kg