For this case we propose a system of equations:
x: Variable representing the plant with pink flowers
y: Variable representing the plant with purple flowers
We have as data that:
![x + y = 15\\8x + 5y = 96](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v8q7xa79jzk2x2rsqgz24baip2dy8yxi67.png)
From the first equation we have to:
![x = 15-y](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ya9quo8zpt8drhuatzobasqfgfbu4g7fzm.png)
Substituting in the second equation:
![8 (15-y) + 5y = 96\\120-8y + 5y = 96\\-3y = 96-120\\-3y = -24\\y = \frac {-24} {- 3}\\y = 8](https://img.qammunity.org/2020/formulas/mathematics/middle-school/uzwgkw4fdt0n1dq1vc5s0avb93ao8g40ay.png)
Arianna bought 8 purple flowers.
Now we have:
![x = 15-8\\x = 7](https://img.qammunity.org/2020/formulas/mathematics/middle-school/l7b9yci52jk37qqyiguoodbtijaxcwmdmn.png)
Arianna bought 7 pink flowers.
Answer:
Arianna bought 7 pink flowers.