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

Hence, Amber use 30 feet of basic tiles and 6 feet of decorative tiles.