a)
17,8•{4,5•[12/2•(232,4-64,8•3,25)-249,16]-x}=281,24
17,8•{45/10•[6•(232,4-210,6)-249,16]-x}=281,24
17,8•[9/2•(6•21,8-249,16)-x]=281,24
17,8•[9/2•(130,8-249,16)-x]=281,24
17,8(-9/2•118,36-x)=281,24
1065,24/2-x=281,24/17,8
532,62-x=15,8
x=532,62-15,8=516,82