Let
x-------> Amy's monthly rent
y-------> Amy's monthly income
we know that
[tex]x= \frac{1}{4}y[/tex] -----> equation 1
[tex]x=\$1200[/tex] -----> equation 2
substitute equation 2 in equation 1
[tex]1200= \frac{1}{4}y\\ y=4*1200 \\y=\$4,800[/tex]
therefore
the answer is
Amy's monthly income is [tex]\$4,800[/tex]