A = 12/5 - 3/5 * 7/4
= 12/5 - 21/20
= 48/20 - 21/20
= 27/20
B = ( 3/4 + 1/3 ) : ( 7/5 - 1/2 )
= ( 9/12 - 4/12 ) : ( 14/10 - 5/10 )
= 5/12 : 9/10
= 5/12 x 10/9
= 50/108
= 25/54
C = 6 * 10^-7 * 15 * 10^11 sur 8 * ( 10^2 )^4
= 3/5 000 000 * 1,5 * 10^12 sur 800 000 000
= 1,125 * 10^-27