Question 152052
You are asked to find three sequential numbers with a sum of 60

Let x be the first number
The x+1 is the second number
And x+2 is the third one

{{{x + (x+1) + (x+2) = 60 }}}
{{{3x + 3 = 60}}}
{{{3x = 57}}}
{{{x = 19}}}
x+1 = 20
x+2 = 21

So you have the numbers correctly. 

To verify your answer, just add then three numbers and see if they equal 60
Does  {{{x + (x+1) + (x+2) = 60 }}} when x=19?
{{{ 19 + 20 + 21 = 60}}}
{{{ 60 = 60}}} which is true. So those numbers work!

WTG