Replacing a with 6 in the first expression:
7, 8(6)+2, 3(6)-5(6)
7, 48+2, 18-30
7, 50, -12

Replacing b with 46 in the second expression:
2(0, 3(46)+5)+1, 4(46)
2(0, 138+5)+1, 184
2(0, 143)+1, 184
0, 286+1, 184
0, 144, 184

Replacing a with 1 in the third expression:
54(b+0,8)+1, 7(2,3)+1
54(2,3)+1, 7(2,3)+1
124+1, 16+1
125, 17

Replacing b with 2,3 in the fourth expression:
46(1+2,5)-2, 8(1+2,5)
46(3,5)-2, 8(3,5)
161-2, 34
159, 34