[tex]\bf \begin{cases} a+b=-1\\ x+y+z=2 \end{cases} \\\\[-0.35em] ~\dotfill\\\\ \begin{array}{llll} 7a+7b\qquad &+6z+6x+6y\\\\ 7(a+b)&+6(z+x+y)\\\\ 7(a+b)&+6(x+y+z)\\\\ 7(-1)&+6(2)\\\\ -7&+12&\implies 5 \end{array}[/tex]
Answer:
5
Step-by-step explanation:
hihi, so the key to this is manipulating the equations. Realizing that 7a + 7b is just 7*(a+b) makes this fairly simple since you already know what a+b equals and just have to multiply that by 7. Same goes with x, y, and z. 6x + 6y + 6z is the same as 6(x + y + z). Thus, -1 * 7 + 2 * 6 = 5
