Let [tex]A[/tex] be the number of 49 cent stamps bought and [tex]B[/tex] be the number of 34 cent stamps bought. We can set up the following equations using the information above:
[tex]A + B = 26[/tex]
[tex]0.49A + 0.34B = 11.39[/tex]
Substituting the first equation into the second equation will give you the following:
[tex]0.49(26 - B) + 0.34B = 11.39[/tex]
Solving for B will give you the number of 34 cent stamps purchased, and then you can figure out the number of 49 cent stamps purchased.