Answer:
- C. infinitely many solutions
Explanation:
We can tell that an equation has multiple/ infinitely many solutions if we try to solve it and get a variable or a number equal to itself.
Let's solve the given equation and see what we'll get :-
![\sf 15-10b-6=-10b+9](https://img.qammunity.org/2023/formulas/mathematics/high-school/ngkhu4gsxmbstfdd00i83hdi239dp89mvp.png)
Add 10b to both sides:-
![\sf 15-10b-6+10b=-10b+9+10b](https://img.qammunity.org/2023/formulas/mathematics/high-school/62yu9juk5hxdtb66h5qli5devid4rt0yrk.png)
Simplify:-
![\sf 15-6=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/24rg8x8441mc5slwgwcc1wlronwhztx3nz.png)
Subtract:-
![\sf 15-6=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/24rg8x8441mc5slwgwcc1wlronwhztx3nz.png)
![\sf 9=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/c7vmna3zrotc4v8bl178rqexc3kk1inklx.png)
As we can see, both sides ended up equal, therefore, this equation has infinitely many solutions!
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Hope this helps!
Have a great day!