Salut :)
A=2+1/2/5-2/7
=2+(1/2)x(1/5)-2/7
=2+1/10-2/7
=35/70+7/70-20/70
=22/70
=11/35
B=(((10/7)-(4/6)x2-(1/2)/(1/5))/2)/3
=(((10/7)-(8/6)-(1/2)x5))/2)/3
=(((10/7)-(8/6)-(5/2))/2)/3
=(((60/42)-(56/42)-(105/42))/2)/3
=((-101/42)/2))/3
=((-101/42)x(1/2))/3
=(-101/84)/3
=(-101/84)x(1/3)
=-101/252
Voila :)