We are given the expression
![\frac{10c+6}{7c\text{ -5}}](https://img.qammunity.org/2023/formulas/mathematics/college/w0zh3i7gbqu7qnk0piwd8rxn7oa02ir95r.png)
and we want to find the value of c for which this expression is undefined. Note that for rational expressions, they are undefined when we are dividing by 0. So, to find the value of c to which the expression is undefined, it suffices to find the value of c for which the denominator is 0. So we have the following equation
![7c\text{ -5=0}](https://img.qammunity.org/2023/formulas/mathematics/college/f1qhjzt7gkrdvufxzjvvrc6z25vxie16l5.png)
Now, we add 5 on both sides, so we get
![7c=5](https://img.qammunity.org/2023/formulas/mathematics/college/kwjxkmxx2wsx912saxb7rxet7ja0374flz.png)
Finally, we divide both sides by 7. So we have
![c=(5)/(7)](https://img.qammunity.org/2023/formulas/mathematics/college/6odh0f62dupponv0z9mw25jz9pcj2t3lnn.png)
so when c=5/7 the expression is undefined