Which is the best estimate for (6.3 times 10 Superscript negative 2 Baseline) (9.9 times 10 Superscript negative 3 Baseline) written in scientific notation? 6 times 10 Superscript negative 4 60 times 10 Superscript negative 5 6 times 10 Superscript 7 60 times 10 Superscript 6