The mass is 5kg
I hope this helps
✧・゚: *✧・゚:* *:・゚✧*:・゚✧
Hello!
✧・゚: *✧・゚:* *:・゚✧*:・゚✧
❖ In order to keep the bench from conducting heat, Shane could build it out of wood. Wood doesn't conduct heat so this would work best for Shane.
~ ʜᴏᴘᴇ ᴛʜɪꜱ ʜᴇʟᴘꜱ! :) ♡
~ ᴄʟᴏᴜᴛᴀɴꜱᴡᴇʀꜱ

Actually Welcome to the Concept of the Acceleration.
a = V2-V1/t
so the correct answer is, a = ∆v/t
option C.) is correct, a = ∆v/t