It looks like the equation is
3^x + 2x^5 = 405
and you want to solve for x.

What to know:
- For x ≤ 0 the left-hand side is ≤ 1, so no solution there.
- For x > 0 the function f(x) = 3^x + 2x^5 is strictly increasing, so there is a unique real solution.

Numerical solution (rough approach):
- f(2.85) ≈ 3^2.85 + 2*(2.85)^5 − 405 ≈ -6
- f(2.86) ≈ 3^2.86 + 2*(2.86)^5 − 405 ≈ +0.9

So the root lies between 2.85 and 2.86. A more precise estimate (e.g., via Newton’s method) gives

x ≈ 2.8588 (to four decimals)
x ≈ 2.859 (to three decimals)

Check: 3^2.859 ≈ 23.13 and 2*(2.859)^5 ≈ 382.0, sum ≈ 405.

If you actually meant a different expression (for example, 3^x + 2x5 interpreted as 3^x + 10, or 3^x + 2x5 with some other meaning), please clarify and I’ll adjust the solution.