35 m x 3 = 105m = 110m
By significant digits rules of multiplication, this would be 110m. (The 35m has 2 sigfigs and 3 has infinite because it is a countable number)
35m + 35m + 35m = 105m
By significant digits rules of addition, this would be 105m (All numbers are significant to unit place)
Am I missing something? I can’t imagine the precision of your answer being increased by your choice of adding the number 3 times instead of multiplying by 3.