Help with vectors problems

[spark sorrel]

find where the line east at 8 45 and the line north east at 9 intersect

might be a better way, say at 8:45 its at ai+bj then i know the lighthouse is at ai+cj

then if its at pi+qj at 9 then the lighthouse must be at some (p+n)i+(q+n)j

a=p+n, so you can find n