Help!! Granddaughters homework Don't know where to start

Reedee said:
If 5*3=4
2*8=2
and 6*3=3
What is the value of 1*7
Is that some kind of puzzle?
1*7=4

The 3 digits add up to 12 .

That's a guess!
 
Thank you Denis!! I told my granddaughter to tell her math teacher that it's not nice to confuse old ladies!!
 
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