Never seen that calculation before. How can the left side of the equation equal 5.8 when 5.8 appears on the right side.
Without any other info this is obviously mathematically impossible with x not equal to 0.
(pH =5.8+x)
How can pH equal 5.8 unless x = 0. Where does 5.8 as a constant come from in the equation?
In addition this is not enough data to calculate pH to the best of my knowledge.
Where are you getting the formula from?