I have a system with four motor 50 HP, 40 HP, 5 HP, and 7.5 HP. Tell me MCB rating for that system.

What does MCB mean to you?

Main Circuit Breaker?

Need to know the voltage of the system to arrive at the amp draw.

Where are you located? This will help determine which Code or Standard applies.

What is your country?
Standard used?. NEC/BS/VDE etc
Voltage/Frequency? 110/220V,50/60Hz
Fault level (kA) at switchboard?
Type of load?. constant,variable,fluctuating,periodical... pump/fan,elevator,compressor,conveyor
Duty type? AC! 2,3 etc S1,S2,S3 etc
Type of Load connected to each motor?
Starter used for each motor? DOL/star-delta(open/closed transition),VSD,Primary R or L,slip ring..
In your country what is the maximum kW of motor allowed in DOL starting?