Answer:
-2
Explanation:
Let Oliver's number be x.
He multiplies it by 5:
x * 5 = 5x
He then subtracts 26:
5x - 26
Then, he divides by 6:
He then multiplies his original number by 3, and gets the same answer.
This implies that:

Let us simplify this:

Collecting like terms:

Oliver's number is -2.