Answer: We first remove the innermost grouping symbol ( ), then{ } and then [ ]
We have
86−[15x−7(6x−9)−2{10x−5(2−3x)}]
=86−[15x−42x+63−2{10x−10+15x}]
=86−[15x−42x+63−20x+20−30x]
=86−15x+42x−63+20x−20+30x
Rearranging and collecting the like terms, we get:
=86−63−20−15x+42x+20x+30x
=3+77x