To solve this equation, we first need to find the number of terms in the series. The series starts with x+4 and ends with x+26, with each term increasing by 2.

The nth term of an arithmetic series can be found using the formula:
an = a1 + (n-1)d

where an is the nth term, a1 is the first term, n is the number of terms, and d is the common difference.

In this case, a1 = x+4, d = 2, and an = x+26. Plugging these values into the formula, we get:
x+26 = x+4 + (n-1)2
x+26 = x+4 + 2n - 2
x+26 = x+2n+2
2n = 24
n = 12

So, there are 12 terms in the series.

Next, we can find the sum of the series using the formula for the sum of an arithmetic series:
Sn = n/2 * (a1 + an)

Plugging in the values we know, we get:
210 = 12/2 * (x+4 + x+26)
210 = 6 * (2x + 30)
210 = 12x + 180
30 = 12x
x = 2.5

Therefore, the value of x is 2.5.