Calculer à et b et donner l'écriture de c

Bonjour , 
A = 7/5 + 3/5 × 11/6
A = 7/5 + 33/30
A = 42/30 + 33/30
A = 75/30
A = 15/6 
B = 6/5 ÷ (1/15 - 1/5 ) 
B = 6/5 ÷ ( 1/15 - 3/15 ) 
B = 6/5 ÷ ( -2/15)
B = 6/5 × 15/-2
B = 90/ -10
B = -9 
C = 4×10¹⁴×12 / 3×10¹¹
C = 48 × 10¹⁴ / 3 × 10¹¹
C = 48/3 × 10¹⁴⁺(⁻¹¹)
C = 16 × 10 ³
C = 1,6 × 10 ⁴