А)6-7а,так как -5а-7а+4а+а=-7а
б)-7n-1,так как 5n-10-6n-18-6n+27=-7n-1
0.756²-0.241*0.756-0.415*0.756=0.756(0.756-0.241-0.415)=0.756*0.1=0.0756
0.25²*2.4+0.25*2.4²-0.25*2.4*0.65=0.25*2.4(0.25+2.4-0.65)=0.25*2.4*2=0.5*2.4=1.2
2.49*1.63-2.12*1.63+1.63²=1.63(2.49-2.12+1.63)=1.63*2=3.26
0.16*6.41*1.25-0.16*1.25²-0.16²*1.25=0.16*1.25(6.41-1.25-0.16)=0.16*1.25*5=1
13а-23-5а=9
13а-5а=23+9
8а=32
а=4
Ответ: 4