Area of a parallelogram is:
[tex]\sf A=bh[/tex]
Where 'b' is the base and 'h' is the height. Plug in what we know:
[tex]\sf A=(x+4)(x+3)[/tex]
Distribute(multiply everything in the first parenthesis to everything in the second parenthesis):
[tex]\sf x\times x=x^2[/tex]
[tex]\sf x\times 3=3x[/tex]
[tex]\sf 4\times x=4x[/tex]
[tex]\sf 4\times 3=12[/tex]
So we have:
[tex]\sf A=x^2+3x+4x+12[/tex]
Combine like terms(3x + 4x = 7x):
[tex]\sf A=\boxed{\sf x^2+7x+12}[/tex]
