A rectangle has a length 3L and a height L. A charge of magnitude q is placed at the upper left corner, and another charge of magnitude Q is placed at the lower right comer. The electric field at the (empty) lower left corner is directed along the diagonal line that runs north of east through the two empty corners. 

(a) Do the charges, q and Q, have the same polarity? Explain.  

(b) Find the ratio Q/q.