Ravi,
You are not going to put the formula anywhere when you run MCJB report. When the Report runs it uses the formula's to calculate the MTTR & MTBR for the Equipment. You do not need to enter the formula anywhere.
The formula used in MCJB report to calculate MTTR & MTBR for Equipment is explained at the link below. Check "Key Figures for Breakdown Statistics":
http://help.sap.com/saphelp_47x200/helpdata/en/c1/37699d449a11d188fe0000e8322f96/frameset.htm
Note:You will need atleast few Breakdown Notifications created for the Equipment to see any result in the MCJB report.
Hope that helps!
Thanks.
Wankash.