Answer:
[tex]\huge\boxed{x=5}[/tex]
Step-by-step explanation:
[tex]\left\{\begin{array}{ccc}7x-4y=23\\x+y=8&|\text{subtract}\ x\ \text{from both sides}\end{array}\right\\\left\{\begin{array}{ccc}7x-4y=23&(1)\\y=8-x&(2)\end{array}\right\\\\\text{substitute (2) to (1):}\\\\7x-4(8-x)=23\qquad|\text{use the distributive property}\\\\7x+(-4)(8)+(-4)(-x)=23\\\\7x-32+4x=23\qquad|\text{combine like terms}\\\\(7x+4x)-32=23\qquad|\text{add 32 to both sides}\\\\11x-32+32=23+32\\\\11x=55\qquad|\text{divide both sides by 11}\\\\\dfrac{11x}{11}=\dfrac{55}{11}\\\\x=5[/tex]
