Problem 5.1. Sasha wrote down on the board all two-digit numbers divisible by 6, and then erased those that do not end in 4. What is the largest number that ended up on the board?
Answer: 84.

Solution. Let's take the largest two-digit number divisible by 6, which is 96, and sequentially subtract 6 from it. This way, we will go through all numbers divisible by 6 in descending order. We will stop at the first one that ends in 4, which is what we need.

$$
96 \rightarrow 90 \rightarrow 84
$$