How do you know when two quantities vary directly

Two quantities vary directly if;
i) An increase in one quantity leads to proportional increase in the second quantity
ii) A decrease in one quantity leads to a proportional decrease in the second quantity

You can find the area of a rectangle by multiplying the length and height. so multiply 1/2*7/4(which is the simpler version of 1 3/4) and you get 7/8 as your answer.