Question

How do you check a linear equation and find if 7 is a solution to `5x-5=30`?

Answer 1

In general, to evaluate any function `f(x)` in a specific point, you simply need to substitute every `x` with that specific value.

In your case, rather than evaluating a function, you want to check an identity. The spirit is the same, you only need to substitue `x \rightarrow 7`, and see if you obtain a true statement, or a false one.

Substituting, we have
`5x-5=30 \rightarrow 5\cdot 7 -5 =30 \iff 35-5=30 \iff 30=30`
which is of course true.