the sum of 2 times a number and -2, added to 4 times a number

[math_celebrity]

the sum of 2 times a number and -2, added to 4 times a number.

The phrase, a number, means an arbitrary variable, let's call it x.

2 times a number
2x

The sum of means add, so we add -2, which is the same as subtracting 2
2x - 2

Now, we add 4 times x
2x - 2 + 4x

Combining like terms, we have:
(2 + 4)x - 2
6x - 2