Brackets are used to control the priority of calculations, just as they do in arithmetic.
An expression such as `4(x + 3)` means that the 4 multiplies both the `x` and the 3. Brackets are a bit like paper bags: there is `x + 3` in each bag, and if there are 4 bags then there are 4 lots of `x` and 4 lots of 3.
Removing the brackets is called expanding the expression, or expanding the brackets. Each term in the brackets has to be multiplied by the term outside the bracket
`4(x + 3)`
`= 4 xx x + 4 xx 3`
`= 4x+ 12`
Expand `3(2x - 7)`
`3(2x - 7)`
`= 3 xx 2x - 3 xx 7` `= 6x - 21`
Answer: `6x - 21`
Expand `3a(2a + 4) + 6a`
Expand the brackets:
`3a xx 2a + 3a xx 4 + 6a`
`= 6a^2 + 12a + 6a`
`= 6a^2 + 18a`
Answer: `6a^2 + 18a`
See also Using Brackets