You can put this solution on YOUR website! I don't think it's possible to insert parentheses to make this a true expression...here's why:
+/- 10 and +/-2 are both congruent to 2 modulo 4, while -8 is 0 modulo 4. The left side becomes 2 + 0 + 2 + 2 = 6 = 2 modulo 4, regardless of where parentheses are placed. However, 4 is 0 modulo 4 so the two expressions must carry different residues and cannot be equivalent.