2,5х+12=2х-13
/-7.2/; -7.1; 7.(2); 23/3
51/4(12-(-0.4))+31/4(-(-0.4)-8)=
=51/4(12+0.4)+31/4(0.4-8)=
=51/4×12.4+31/4×(-7.6)=
=51/4×62/5+31/4×(-38/5)=
=51/2×31/5-31/2×19/5=
=1581/10-589/10=
=496/5=99,2
Б) 3/8+(-14/9 + 5/8)
3/8+(-67/72)
-5/9
Е) -9,7+(-8,3)+3,8
-9,7-8,3+3,8
-14,2