Use formula r = log( i / i sub zero)
sub-zero being like an just below. don't know the
r = ritcher number of earthquake
i = intensity of earthquake
i sub-zero = intensity of minimum detectable earthquake

an earthquake has a richter number of 4.2. how many times more intense than the minimum detectable earthquake is the earthquake? round your answer to the nearest whole number.

answer: #1 ads up by 8 and i don't know #2

large crystals result from very slow cooling.

evaporation of water: this would produce an evaporite which is a sedimentary rock. like a salt pan in a desert. not possible to have volcanic rocks originate this way.

crystalization in molten earth: slow cooling over time. (hundreds to millions of years)

crystalization at earth's surface: this results in fast cooling. (a few hours to a few months or years)

crystalization from cooling off hot water: that would be a hydrothermal deposit. while associated with volcanics they are not volcanic rocks themselves and usually occur fairly rapidly.