1. The problem statement, all variables and given/known data The magnetic field in a certain region is given by B=<40i-18k>T. How much flux passes through a 5cm^2 area loop in this region if the loop lies flat in the xy plane? 2. Relevant equations Flux=B.A 3. The attempt at a solution I got the answer (90 * 10^-4) in negative, and its in positive in the textbook at the back... How can flux be negative and why can we drop the negative sign?