We want to solve the following system of equations
[tex]x+y=14[/tex]and
[tex]4x+y=38[/tex]where x is the number of adult tickets sold and y is the number of child tickets sold.
From the first equation, we can deduce that
[tex]y=14-x[/tex]If we replace this value on the second one, we get
[tex]4\cdot x+(14\text{ -x)=38}[/tex]If we operate on the left hand side, we get
[tex]4x\text{ -x +14 = 3x+14=38}[/tex]Then, if we subtract 14 on both sides, we get
[tex]3x=38-14=24[/tex]Finally, if we divide both sides by 3, we get
[tex]x=\frac{24}{3}=8[/tex]If we replace this value in the original equation, we have that
[tex]y=14-8=6[/tex]So 8 adult tickes and 7 child tickets were sold in total.