The most important rule with puzzles like this is simple: don’t assume the final line is identical to the earlier ones.

Start with the first equation and determine the value represented by each object or symbol. Then use the second and third equations to calculate the remaining values.

But before solving the final expression, stop.

Look carefully for changes. Is there one object instead of two? Has an accessory disappeared? Is an object facing another direction? Has the mathematical operation changed?

These small differences are often deliberately included to catch people who solve the puzzle from memory instead of examining what’s actually shown.

There’s another common trap: order of operations.

If the final expression contains multiplication together with addition or subtraction, multiplication normally comes first unless parentheses indicate otherwise.

For example, if the final line effectively becomes:

A + B × C

you calculate B × C first, then add A.

That’s why simply working from left to right can produce the wrong result.

I couldn’t verify the actual puzzle image or its published solution from the linked page, so I won’t invent a numerical answer.

The real trick is observation first, calculation second.

Take one more look at the original image before checking anyone else’s answer.

What answer did you get on your first attempt?