Answer:
A:
![7x+y=801](https://img.qammunity.org/2019/formulas/mathematics/middle-school/t6kq9qu80kfg6mp4cg8wxibxgssrpkimmu.png)
B:
![18x+3y=1949](https://img.qammunity.org/2019/formulas/mathematics/middle-school/uv1mljtf1529w35dggj889bhhd2ais2p0g.png)
Explanation:
we are given system of equations as
![84x+12y=9612](https://img.qammunity.org/2019/formulas/mathematics/middle-school/3bijlk0ijnj20zdqur8i1felgbb89a7gek.png)
![126x+21y=13643](https://img.qammunity.org/2019/formulas/mathematics/middle-school/pxfqd6nxhz1kp9txof9ro0sjpk346ggpas.png)
We can simplify each system of equations
![84x+12y=9612](https://img.qammunity.org/2019/formulas/mathematics/middle-school/3bijlk0ijnj20zdqur8i1felgbb89a7gek.png)
we can factor out common terms
![12* 7x+12* y=12* 801](https://img.qammunity.org/2019/formulas/mathematics/middle-school/tbyvfhay5mbbw262gjei0p036jbu6vqzny.png)
![12(7x+y)=12* 801](https://img.qammunity.org/2019/formulas/mathematics/middle-school/b42q8fe2e1taiwjzddxo0a1eof1kpf9znb.png)
we can divide both sides by 12
![7x+y=801](https://img.qammunity.org/2019/formulas/mathematics/middle-school/t6kq9qu80kfg6mp4cg8wxibxgssrpkimmu.png)
now, we can simplify second system of equation
![126x+21y=13643](https://img.qammunity.org/2019/formulas/mathematics/middle-school/pxfqd6nxhz1kp9txof9ro0sjpk346ggpas.png)
Firstly, we can factor
![7* 18x+7* 3y=7*1949](https://img.qammunity.org/2019/formulas/mathematics/middle-school/dc11jyk0pad5k8saogsnb6o066kaw0r2n0.png)
![7(18x+3y)=7*1949](https://img.qammunity.org/2019/formulas/mathematics/middle-school/lk4p4r84owd174054xnch9kd26jmdo9wby.png)
we can divide both sides by 7
![18x+3y=1949](https://img.qammunity.org/2019/formulas/mathematics/middle-school/uv1mljtf1529w35dggj889bhhd2ais2p0g.png)
so, we get
A:
![7x+y=801](https://img.qammunity.org/2019/formulas/mathematics/middle-school/t6kq9qu80kfg6mp4cg8wxibxgssrpkimmu.png)
B:
![18x+3y=1949](https://img.qammunity.org/2019/formulas/mathematics/middle-school/uv1mljtf1529w35dggj889bhhd2ais2p0g.png)