API 650 5.10.5.1 Formula

[VigneshK]

Dear experts,
can you explain formula given in sec 5.10.5.1 for nominal thickness calculation of roof plate. what x stands for? what is the value of x i need to give?

 

[IFRs]

In this case, I believe that lowercase "x" means "times" or "multiply" and does not represent a variable or constant.