Answer :
Let
x--------> Juanita's allowance
we know that
1) Juanita spent [tex]3/4[/tex] of her allowance at the mall
so
Juanita spent at the mall --------> [tex]\frac{3}{4}x[/tex]
2) Of the money spent at the mall, [tex]1/2[/tex] was spent on new earphones
so
Juanita spent on new earphones ------->[tex]\frac{3}{4}x*(1/2)=\frac{3}{8}x[/tex]
therefore
the answer is
Juanita spend on earphones [tex]\frac{3}{8}[/tex] of her allowance