Question

Y+x=21
Calcule x e y

Answer 1

${4\over10}={x\over y}~~~~sendo~~x+y=21\\ \\ isola~~x=21-y\\ \\ substituir\\ \\ {4\over10}={21-y\over y}\\ \\ 4y=10(21-y)\\ \\ 4y=210-10y\\ \\ 4y+10y=210\\ \\ 14y=210\\ \\ y=210\div14\\ \\\fbox{ y=15 }$

Se

x=21-y

x=21-15

x=6