Answer:
-  first number = 89
- second number = 534
- third number = 189
Explanation:
Let the first number be x
Given second number is 6 times a first number.
If first number is x then second number is 6*x = 6x 
Given third number is 100 more than the first number
If first number is x then third number is x+100 = x+100
Sum of these three numbers in terms of x 
is 
sum = x+ 6x+x+100 = 8x+100 __________1
Given, that sum of these numbers is 812.
equating 812 with equation 1 we have,
8x+100 = 812
=> 8x = 812- 100
=> 8x = 712 
=> x = 712/8 = 89.
Therefore,
 first number = x = 89
second number = 6x = 89*6= 534
third number = x+100 = 89+100 = 189