Let n + 1 = the second consecutive number, and ...
Let n + 2 = the third consecutive number.
Since we're given that: "the sum of three consecutive numbers is 210," then we can now translate this statement mathematically into the following equation to be solved for the unknown number n: n + (n + 1) + (n + 2) = 210
n + n + 1 + n + 2 = 210
Collecting like-terms on the left, we get: 3n + 3 = 210
I got 2.527. And the 7 repeats I’m wasn’t sure if you wanted it in a fraction but it shouldn’t be difficult to convert if you have a calculator with that function