1.
a, 2x + (-61) - (21-61)
= 2x - 61 - 21 + 61
= 2x + ( 61-61) -21
= 2x -21
b, (-3 - x + 5 ) +3
= -3 - x + 5 + 3
= ( -3 + 3 ) + 5 - x
= 5 - x
2.
a, x + (-81) - ( 11 - 81)
= x - 81 - 11 + 81
= x -11 + ( 81 - 81)
= x - 11
b, ( -1 - x + 2 ) + 1
= -1 - x + 2 + 1
= ( -1 + 1) + 2 - x
= 2 - x
c, 15 - (11 -x) + (11 - 15)
= 15 - 11 + x + 11 - 15
= ( 15 -15 ) + (11 -11) + x
= x
d, 15 - (15 - x + 202) + 202
= 15 - 15 + x - 202 + 202
= (15 -15) + (202 - 202) + x
= x