56:4+2•(120:6-80:20)+17•8
= 56 + 2•(20-4) + 17•8
= 56 + 2•16 + 136
= 56 + 32 + 136
= 88 + 136
= 224

Therefore, 56:4+2•(120:6-80:20)+17•8 = 224.