A daytime telephone call from Washington to Melbourne ,Australia costs 5 cents for the first minute and 6.5 cents for each additional minute. Solution a)1 b)1 c)0 (a1/a2=b1/b2 !=c1/c2) d)infinitely many e)infinitely many(a1/a2=b1/b2=c1/c2=d1/d2) f)0 (the third plane is parallel to the other 2) g)infinitely many (two planes are superimposed while one is not, so the intersection is a line which has infinite points).