3 times a number is written as 3x ( where x is the number).
25 less than that becomes 3x-25
then it is at least 26, which means it is at least 26 or bigger
3x-25 ≥ 26
Now solve for x:
Add 25 to each side:
3x ≥26 +25
3x ≥ 51
Divide both sides by 3:
x ≥51 / 3
x ≥ 17