To solve the equation \( 715 + 15(8 + x) = 730 \), follow these steps:

1. Distribute the 15 inside the parentheses:
\[
715 + 15 \cdot 8 + 15 \cdot x = 730
\]

2. Calculate \( 15 \cdot 8 \):
\[
15 \cdot 8 = 120
\]

3. Substitute back into the equation:
\[
715 + 120 + 15x = 730
\]

4. Combine the constants on the left side:
\[
835 + 15x = 730
\]

5. Subtract 835 from both sides to isolate the term with \( x \):
\[
15x = 730 - 835
\]

6. Calculate \( 730 - 835 \):
\[
730 - 835 = -105
\]

7. So, the equation now is:
\[
15x = -105
\]

8. Divide both sides by 15 to solve for \( x \):
\[
x = \frac{-105}{15}
\]

9. Simplify the fraction:
\[
x = -7
\]

So, the solution to the equation \( 715 + 15(8 + x) = 730 \) is \( x = -7 \).