B. 1/40…. You divide 1/2 by 20 to find out how much hand sanitizer was used on each desk. You can keep change flip meaning keep the 1/2 change the division to multiplication and flip the 20 to 1/20 then multiply. 1/2 by 1/20 which equals 1/40.
Differentiate the given solution:
Substitute 
and 
into the ODE:
and it's easy to see the left side indeed reduces to 0.
Answer:
D. is the correct one.........
Answer:
Turn off battery supply → The electromagnet turns off.
Place a magnet care inside the coil of wire → The strength of the electromagnet increases.
Change the direction in which the current flows → The poles of the electromagnet reverses
