x = 6
given x varies inversely with y then
xy = k ← k is the constant of variation
to find k use the condition x = 4 when y = 9, hence
k = 4 × 9 = 36
x = [tex]\frac{36}{y}[/tex] ← inverse variation equation
when y = 6, then x = [tex]\frac{36}{6}[/tex] = 6
