First you need to expand it by multiplying what is in the brackets by what is in front of them so it would become:
4x*x=4x^2 and 4x*3= 12x so it is 4x^2+12x+7x
Now we can simplify by adding the like terms (the terms with the same variable) So it is:
12x+7x=19x
4x^2+19x
Hope this helps :)
