`A=[ \frac{12 +12/13 - 12/7 }{4- 4/7 + 4/13} : \frac{3/19 + 3/21}{91/19}] . \frac{40 . 50 + (-1)^2}{40+ 50 + (-1)^2`
`A = [ \frac{12(1 + 1/13 - 1/7)}{4(1 - 1/7+1/13)}] : \frac{3(1/19+1/21)}{91(1/19 + 1/21)] . \frac{2001}{91}`
`A = [ 12/4 : 3/91] . \frac{2001}{91}`
`A = [ 3 × 91/3] . 2001/91`
`A = 91 . 2001/91`
`A = \frac{91 . 2001}{91}`
`A = 2001`
