Here the given expression is
[tex] y =(\frac{3}{4})^x [/tex]
We need to find the value of y when x =3 . So we substitute the value of x in the given expression.
[tex] y =(\frac{3}{4})^3 = \frac{27}{64} =0.4 [/tex]
So when x=3, y=0.4 and that's the required answer.