21+32−(14+20−5)+15−(8+4−5)+8−2−30
=53−(14+20−5)+15−(8+4−5)+8−2−30
=53−(14+15)+15−(8+4−5)+8−2−30
=53−29+15−(8+4−5)+8−2−30
=24+15−(8+4−5)+8−2−30
=24+15−(12−5)+8−2−30
=24+15−7+8−2−30
=24+8+8−2−30
=32+8−2−30
=32+6−30
=38−30
=8
[tex]21+32−(14+20−5)+15−(8+4−5)+8−2−30=53−(14+20−5)+15−(8+4−5)+8−2−30 \\ =53−(14+15)+15−(8+4−5)+8−2−30 \\ =53−29+15−(8+4−5)+8−2−30 \\ =24+15−(8+4−5)+8−2−30 \\ =24+15−(12−5)+8−2−30 \\ =24+15−7+8−2−30 \\ =24+8+8−2−30 \\ =32+8−2−30 \\ =32+6−30 \\ =38−30 \\ \color{darkgreen}\boxed { =8}[/tex]