{2(x+5)=9-3(4+y) {21+6x+4y=4(2x+5) это система уравнений  

2x+10=9-12-3y 21+6x+4y=8x+20   2x+3y=-13 -2x+4y=-1   7y=-14 x=-2     2x+3*(-2)=-13 2x=-13+6=-7 x=-3.5 Ответ: (-3.5;-2)    

2х+10=9-12-3у             2х+3у=9-12-10      2х+3у=-13      7у=-14     4*(-2)-2х=-1 21+6х+4у=8х+20         6х+4у-8х=20-21     4у-2х=-1          у=-2         -8-2х=-1                                                                                                                    -2х= 7                                                                                                                      х=-3,5 Ответ: х=-3,5;  у=-2