I don't understand linear programming

"A furniture company makes chairs and sofas. It takes 7 hours to build a chair and 4 hours to build a sofa. It takes 4 hours to upholster a chair and 8 hours to upholster a sofa. There at most 112 hours to build the furniture and at most 144 hours to upholster the furniture. Find the maximum profit if a chair has an average profit of $80 and a sofa has an average profit of $70. Your first order came in for 4 chairs and 7 sofas so you must make at least 4 chairs and 7 sofas"
Will somebody please explain how to graph and answer this question? I don't understand it at all!

If you want to build x chairs and y sofas, then it will take

time to build = B = 7x + 4y
and
time to upholster = U = 4x + 8y

but you will make

profit = P = 80x + 70y

The constraint statements tell you
B (max) = 112
U (max) = 144

To graph, your x-axis will show x (# chairs) and y-axis will show y (# sofas)

draw the straight line 112 = 7x + 4y
draw the straight line 144 = 4x + 8y

also draw the horizontal line y = 7
and the vertical line x = 4

These lines describe a region in x-y.
It turns out that your maximum profit point will lie on one of the corners of this region.

Find the (x,y) for each corner point for the region, then use those values to evaluate P.

The largest value of P is your maximum profit point.