The patch is 16*20=<<16*20=320>>320 square feet
So he needs 320/4=<<320/4=80>>80 patches
The first 10 patches cost 10*10=$<<10*10=100>>100
He gets a discount on the next 80-10=<<80-10=70>>70 patches
They each cost 10/2=$<<10/2=5>>5
So in total they cost 70*5=$<<70*5=350>>350
That means in total he paid 100+350=$<<100+350=450>>450
#### 450