Chong thinks of a number, adds 10 then multiplies the number obtained by 3, and gets 42.
If the number is n then write an equation for this.

A 3(n + 10) = 42.

explanation

Adding 10 to n gives n + 10.
Multiplying the number obtained by 3 gives 3(n + 10).
Making this equal to 42 gives 3(n + 10) = 42.