25 + ( x - 15 ) = 30
x - 15 = 30 - 25
x = 5 + 15
x = 20
91 . 25 - 91 . 13 - 91 . 12
= 91. ( 25 - 13 -12 )
= 91. 0
= 0
64 . 16 + 81 . 84 + 17 . 16
= 16. ( 64 + 17 ) + 81 . 84
= 16 . 81 + 81 . 84
= 81 . ( 84 + 16 )
= 81 . 100
= 8100
~HT~ and ~ T.i.c.k ~
a / 25 + ( x - 15 ) = 30
x + 10 = 30
x = 20
b / 91 . 25 - 91 . 13 - 91 . 12
= 91 . ( 25 - 13 - 12 )
= 0
c / 64 . 16 + 81. 84 + 17 . 16
= 16 . ( 64 + 17 ) + 81 . 84
= 16 . 81 + 81 . 84
= 81 . ( 16 + 84 )
= 8100