Given :
Initial weight of sumo wrestler, I = 90 kg.
Final weight of sumo wrestler, F = 138 kg.
Time taken, T = 8 months.
To Find :
Weight gain per month.
Solution :
Weight gain per month = ( Final weight - Initial weight ) ÷ Total number of month
Therefore, weight gain per month is 6 kg/month.
Hence, this is the required solution.