To solve the equation 3^(x+1) + 3^(x+3) = 810, we can rewrite it as:

3 * 3^x + 9 * 3^x = 810

Combining like terms, we get:

12 * 3^x = 810

Dividing both sides by 12, we have:

3^x = 810/12

Simplifying the right side, we get:

3^x = 67.5

To solve for x, we can take the logarithm of both sides. Let's take the logarithm base 3:

log3(3^x) = log3(67.5)

Using the logarithmic property, we can bring down the exponent:

x = log3(67.5)

Using a calculator, we find that log3(67.5) is approximately 3.5.

Therefore, the solution to the equation is x = 3.5.