Translation:He can't add.
boq is used when reading a mathematical equation; it's more similar to "plus" than to "add".
wej boq loS; chen Soch is "Four plus three equals seven".
Literally, it's "Four allies with three; seven forms."
I suppose a person adding numbers might conceivably boqmoH them (cause them to ally). But we also have the verb chel for "add".
Klingon for the Galactic Traveler gives us the slang word chelwI' someone who deals in finances, accounting, etc. It literally means one who adds, which obviously refers to arithmetic. So chel can be used to refer to arithmetic addition, even if you use boq to recite an equation.