The answer is two (4 -3)
Zero is not a SF
Answer:
a) 
b) x = 4.47 cm
c) 
d) x = 1.48 cm
Explanation:
a) The center of mass is equal to:

Where m is the mass of beads and x is the distances, if x₁ = d₁, x₂ = d₂ and x₃ = d₃

b) If
m₁ = 23g
m₂ = 15 g
m₃ = 58 g
d₁ = 1.1 cm
d₂ = 1.9 cm
d₃ = 3.2 cm

c) The center of the mass of the beads realtive to the center of bead is:

d) 
Tooth fillings are often made of gold or porcelain because these materials are nonreactive.
b. nonreactive.
∑F = ma = (90 kg)(1.2 m/s²) = 108 N = 100 N (1 significant digit)