15. Efectuați:
a) [+4-(-9+5-8):(+6–10+2)]:(-2); b(-94-6+8–7):(-3+9–1)]:(-4);
c) [-8-(-3+9–1):(-7+2+4)]:(-3);
d) (-2+(-7+3+8):(+6–8–2)]:(-3);
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