A mind for numbers, as mentioned below is very good. There is also a good book for the ‘quicker calculation’ called ‘how to calculate quickly’ that is super easy to dive into and get good value from.
https://www.amazon.com/How-Calculate-Quickly-Arithmetic-Mathematics/dp/048620295X
In the past I'd bought a small Dover book that was trying to teach anyone interested how to do fast mental math, with providing the needed methods/tricks and many many many drills to get sharp. I did try for sometime, but then I left it on the side.
Anyhow, this is the book. It might interest someone.
I would have taken that problem and done (60+40) + 7 + 4. going from left to right is kind of an old trick when it comes to adding, subtracting and multiplying. Given, this isn't exactly what seems to be taught in classrooms today, but it's very close.