1. Perimeter (P) of a square is four times the length of a side (a).   Hint Hint       2. The reciprocal of focal length (f) equals the sum of the reciprocals of the object distance (u) and the image distance (v).   Hint       3. Pressure (P) is the force (F) divided by the area (A).   Hint       4. The sum of the magnitude of the interior angles (A) of a convex polygon divided by 180 equals the number of sides (s) decreased by 2.   Hint       5. Force (F) is the product of the mass (m) of a body and its acceleration (a).   Hint       6. The sum of the parallel sides (a and b) of a trapezium is twice the area (A) divided by the distance (d) between the parallel sides.   Hint       7. Amount (A) paid to return a loan is the sum of the principal (P) and interest (I).   Hint