Ello mates uh can yall help me with 19 and 20 -

Which statement best describes the superposition principle? a.) if two in-phase waves arrive simultaneously at a point, their amplitudes add up b.) if two out-of-phase waves arrive simultaneously at a point, their amplitudes add up c.) if two in-phase waves arrive at a point one after another, their amplitudes add up d.) if two out-of-phase waves arrive at a point one after another, their amplitudes adds up

To solve a problem using the equation for kepler ‘s third law , enrico must convert the average distance of mars from the sun from meters into astronomical units . how should he make the conversion ?

Which of the following is not a double-replacement? a.) hno3 (aq) + kho (aq) -> h2o (l) + kno3 (aq)b.) ba(oh)2 (aq) + 2hclo4 (aq) -> ba(clo4)2 (aq) + 2h2o (l)c.) naoh (aq) + hcl (aq) -> h2o (aq) + nacl (s)d.) zn (s) + 2hcl (aq) -> h2 (g) + zncl2 (s)