The variable z is directly proportional to x, and inversely proportional to y. when x is 3 and y is 6, z has the value 9.5. what is value of z when x =8, & y= 12

This is the concept of proportionality, given that z is directly proportional to x and inversely proportional to y then:
zαx/y
z=(kx)/y
where;
k is the constant of proportionality given by:
k=zy/x
but when x=3 and =6 then z=9.5
therefore:
k=(9.5*6)/3
k=19
hence the formula for z will be:
z=(19x)/y
the value of z when x=8 and y=12 will be:
z=(19*8)/12
z=12 2/3