Hello from MrBillDoesMath!
Answer:
104 F = 40 C
Discussion:
9/5C + 32 = F => in our case, F = 104
9/5C + 32 = 104 => subtract 32 from both sides
9/5C = 104 - 32 =>
9/5C = 72 => multiply both sides by 5/9 (the reciprocal of 9/5)
(5/9)*(9/5) C = 72 * (5/9) =>
C = 72*5/9 = 360/9 = 40
Thank you,
MrB