An art gallery hangs 7 small square pictures on a wall. Each square picture has side length 11cm

a.) Write a calculation for the total area of the wall covered by pictures

 y varies directly with x means y =kx
y varies inversely with z means y =k/z .
 with  k  being a constant

 y varies directly with x and inversely with z
y=kx/z
x=15,z=5 so by putting values
18=15k/5
k=6

So the equation that models the relationship is
y=6x/z
y=6*21/7
y=18
hope this helps