Answer:
141 J
Explanation:
The lowest sig digits in a calculation determine the sig dig of the answer
The temps are listed with 3 significant digits and the spec heat is 3 sig digits (the mass has 4 sig digs) .....so answer will need 3 digits
31.91 g * .903 J/g-C * (26.1 - 21.2 C) = 141 J (three sig dig)