Question

What is the first of four consecutive numbers if their sum is 810?

Answer 1

Let x be the first of the four consecutive numbers.

Then x+1 is the second,

and x+2 is the third,

and x+3 is the fourth.

If their sum is 810, then

   x + x+1 + x+2 + x+3 = 810

If you solve that equation for x, you'll have the answer to your question.