Doubt in cenvat credit service tax

X ltd has obtained a cenvat credit of 55,000 by fraud. This is deducted by Central excise officer on March 13,2010. A show cause notice is issued to X ltd on March 15,2010. The Central Excise Officer (after considering representation by X) determines the quantum of tax payable on may 16, 2010 as follows:

Tax payable (Cenvat fraud) 55,000

Interest                                     7,200

Penalty                                     1,10,000

Amt payable                             =1,72,200.

My doubt is how to arrive at Interest amount? I tried but not getting that amount. Please help. Thanks in advance.

This is from reference material and I am a student.