I think I remember hold on let me see if I can solve it
When the force on some area is doubled and the area doesn't change,
then the pressure on that area has doubled.
Given :
The focal length of a concave mirror is 18 cm.
To Find :
The radius of curvature of the concave mirror.
Solution :
We know,

Therefore, the radius of curvature of concave mirror is 36 cm.
Hence, this is the required solution.
Should be an air tight seal
I love science! if you need any more help let me know i cant guarantee i can help but i will try!
The correct answer is "Some substances must be dissolved in water before they can be used".