Let x be the cost of a hamburger kid meal and y the cost of a chicken nugget kid meal
Monday: 6 hamburger kid meals and 7 chicken nugget kid meals for a total of $39:
[tex]6x+7y=39[/tex]Thursday: $42 on 8 hamburger kid meals and 6 chicken nugget meals:
[tex]8x+6y=42[/tex]System of equations:
[tex]\begin{gathered} 6x+7y=39 \\ 8x+6y=42 \end{gathered}[/tex]To solve by elimination:
1- Multiply first equation by 4 and second equation by -3
[tex]\begin{gathered} 4(6x+7y=39) \\ 24x+28y=156 \\ \\ -3(8x+6y=42) \\ -24x-18y=-126 \end{gathered}[/tex]2- Add both equations you get in step 1:
[tex]10y=30[/tex]3- Use the equation you get in step 2 to solve y:
[tex]\begin{gathered} 10y=30 \\ \text{Divide both sides of the equation into 10} \\ \frac{10}{10}y=\frac{30}{10} \\ \\ y=3 \end{gathered}[/tex]4- Use the value of y to solve x:
[tex]\begin{gathered} 6x+7y=39 \\ \\ 6x+7(3)=39 \\ 6x+21=39 \\ \\ \text{Subtract 21 in both sides of the equation:} \\ 6x+21-21=39-21 \\ 6x=18 \\ \\ \text{Divide both sides of the equation into 6:} \\ \frac{6}{6}x=\frac{18}{6} \\ \\ x=3 \end{gathered}[/tex]Solution:
[tex]\begin{gathered} x=3 \\ y=3 \end{gathered}[/tex]Each hamburger meal costs $3 and each chicken nugget meal costs $3