Let's break this up:
let x = the number
"when I triple my number" is the same as
3x
"and add five" is the same as
+5
We combine it to get
3x+5
"I get twenty-six"
=26
combine to get
3x+5=26
Now we just solve:
subtract 5 from both sides to get
3x=21
divide by 3 to get
x=7