use divisibility rule.  3+ 7+8+R = divisible by 3.  18 + R = divisible by 3.  smallest possible number for R is 0, max possible amount for R is 9  3x6=18 - 18 =0 (can be divisible by 3)  3x7=21 -18 = 3  3x 8= 24 -18 =6  3x 9= 27 - 18 = 9  Total = 4 ways. 
If the four-digit number 3P78 is divisible by 3, how many possible values are there for P? 
Options:
a) $$4$$ 
b) $$3$$ 
c) $$5$$ 
d) $$10$$ 
e) None of the above 