Math Help - cross product on undefined to components vector

the question asks to find the ratio between E0 and B0 and the ratio between w and k
?

E and B are on the x-y plane
they are given as verctors without any components dividing
no x direction part,y direction part,z direction part

so when when i use the maxwell equations



i cant do the cross product of B or E
because i dont know what to put in the tererminant whch is calculating the cross product


i tried to make some components by my self
but i get so many variables