a= 9/11-5/4÷11/7
a= 9/11-5/4×7/11
a=9/11-35/44
a= 9×4/10×4-35/44
a= 36-35/11
a=1/11 = 11
b= (-3/8+5/7):(19/28×1/2)
b= (-3/8+5/7):19/56
b= (-3×7/8×7+5×8/7×8 ):19/56
b= -21+40/56:19/56
b= 19/56:19/56
b = 19/56×56/19
b= 1064/1064
b= 1064÷7/1064÷7
b= 152/152
b=152÷4/152÷4
b= 38÷2/38÷2
b= 19/19