Multiply and simplify out theese brackets(x+1)(x+3)

The method in which you do this problem would be to FOIL. First Outer Inner Last. You take the first terms and multiply them. x*x = x^2 (x to the second power). Then you do it with the rest of foil.
x*x = x^2
x*1 = x
x*3 = 3x
1*3 = 3
x^2 + x + 3x + 3 = X^2 + 4x + 3