The perimeter of RSTU can be calculated alone without the help of MNPQ. It would be just 2(4) + 2(3) = 14 units. However, it would be much sensible if you want to find the parameter of the bigger rectangle. Since they are similar, you could use ratio and proportion.
(length/width)∨MNPQ = (length/width)∨RSTU
(x/9) = (3/4)
x = 6.75 units
Thus the perimeter of MNPQ is 2(6.75) + 2(9) = 31.5 units