Answer: Amber use 30 feet of basic tiles and 6 feet of decorative tiles.
Step-by-step explanation:
Let x be the foot of basic tiles and y be the foot of decorative tiles.
Now, according to the question, we have the following equations
[tex]x+y=36\\y=36-x\ .......(1)\\\\8x+20y=36\times10\\2x+5y=90.......(2)\ \ \ [\text{divide equation by 4}][/tex]
Put y=36-x in (2), we get
[tex]2x+5(36-x)=90\\\Rightarrow2x+180-5x=90\\\Rightarrow-3x=-90\\\Rightarrow\ x=30\\\\\Rightarrow\ y=36-30=6[/tex]
Hence, Amber use 30 feet of basic tiles and 6 feet of decorative tiles.