Answer: Amber use 30 feet of basic tiles and 6 feet of decorative tiles.
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
![x+y=36\\y=36-x\ .......(1)\\\\8x+20y=36*10\\2x+5y=90.......(2)\ \ \ [\text{divide equation by 4}]](https://img.qammunity.org/2020/formulas/mathematics/middle-school/t9yueqc3xc3625hix0gcd5odx6ocsovzvs.png)
Put y=36-x in (2), we get
![2x+5(36-x)=90\\\Rightarrow2x+180-5x=90\\\Rightarrow-3x=-90\\\Rightarrow\ x=30\\\\\Rightarrow\ y=36-30=6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/so0hmic3tozihs617zz70u4mdb4haioogm.png)
Hence, Amber use 30 feet of basic tiles and 6 feet of decorative tiles.