7. Find radius and diameter

A sprinkler placed at the centre of a flower garden sprays water covering a circular area. If the area watered is $1386 \ cm^2$, find its radius and diameter.

• radius = 42 cm, diameter = 21 cm
• radius = 20 cm, diameter = 40 cm
• radius = 21 cm, diameter = 42 cm
• radius = 24 cm, diameter = 48 cm