A man deposits ₹ 1800 per month in a recurring deposit account for 2 years. If he gets ₹ 3600 as interest at the time of maturity, find the rate of interest.

Find the value of x so that 2x - 1, 5x - 6, 6x + 2 and 15x - 9 are in continued proportion.

Solid metallic spheres of diameters 12 cm, 16 cm and 20 cm respectively, are melted to form a single solid sphere. Find the radius of the resulting sphere.

Find the equation of the line through the point (-1, -2) and perpendicular to the line 3x + 4y = 5.