Help! I don't understand GRM and how its calculated.

[Paul Winka]

I've been using the BP calculators. 

After I get the output, I am trying to reverse calculate these numbers so I can understand where they came from. I have been able to do that for all the calculations below EXCEPT the gross rent multiplier. How did the calculator come up with 7.38? That number is not even in the ball park. Rents of $1750 each month would mean a home value of $12,915? Thanks for the help. 

[Ned Carey]

The annual income is $21,000 multiply that by 7.38 and it comes to $154,980.  That is the purchase price of $155,000 rounded off.