Most earthquakes and volcanoes occur A. near the center of continents
B. near the center of crustal plates
C. on the edges of continents
D. on the edges of crustal plates

14 days is the half-life of phosphorus-32

i think it's letter a.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.