Make an equation
2x+3x+7x=90
5x+7x=90
12x=90
x=90/12
Now multiply 90/12 times 2 to get the weight of the small bag-15kg
Then multiply 90/12 times 3 to get the weight of the median bag-22.5kg
Lastly multiply 90/12 times 7 toget the weight of the large bag-52.5kg
Small=15kg
median=22.5kg
large=52.5kg