You can do this in Interface Builder:
1) Control-drag from a frame view (e.g. questionFrame) to main View, in the pop-up select "Equal heights".
2)Then go to size inspector of the frame, click edit "Equal height to Superview" constraint, set the multiplier to 0.7 and hit return.
You'll see that constraint has changed from "Equal height to..." to "Proportional height to...".