Write 5.20x10⁻⁹ x 6.69x10⁻⁸ in scientific notation.

a) 3.48x10⁻¹⁶
b) 3.48x10⁻¹⁶
c) 3.48x10⁻¹⁶
d) 3.48x10⁻¹⁶