A = 2/3 - 7/3 ×8/21
A = 2/3 - 7×8 /3*21
A= 2/3 - 56/63
A=2×21/3×21 - 56/63
A= 42/63 - 56/63
A= -14/63
B= (3/4 - 5/6)×3/2
B=( 3×6/4×6 - 5×4/6×4) ×3/2
B= (18/24 - 20/24) × 3/2
B= -2/24 × 3/2
B= -6/48
C= 11÷ (2/3 - 5/2)
C= 11÷ (2×2/3×2 - 5×3/2×3)
C= 11÷ (4/6 - 15/6)
C= 11÷ (-11/6)
C= 11/1 ÷ ( -11/6)
C=11/1× 6/-11
C= 66/-11