Me ayudan por favor con estos ejercicios de álgebra con la 15, 16 y 17

Can someone me out here and the tell me the greatest common factor

Avery’s piggy bank has 300 nickels, 450 pennies, and 150 dimes. she randomly picks three coins. each time she picks a coin, she makes a note of it and puts it back into the piggy bank before picking the next coin.

Divide. –4.2 ÷ 6 = a –0.7 b 0.7 c –7 d 7 me