<h2>
a) Equivalent resistance is 143 Ω</h2><h2>
b) Potential difference is 71.5 V</h2>
Explanation:
When resistors are connected in series, effective resistance is given by

Here
R₁ = 21Ω
R₂ = 58Ω
R₃ = 64Ω
a) 
Equivalent resistance is 143 Ω
b) We know
Potential difference = Current x Resistance
V = IR
I = 0.5 A
R = 143Ω
Substituting
V = 0.5 x 143 = 71.5 V
Potential difference is 71.5 V
Passengers in an aircraft are subject to the Normal and Gravity Force acting on them at a low 'orbit', so tiny that it can be many times compared to the same surface of the earth when speaking in general terms.
In a high orbit space vehicle or in the same space, said force decreases considerably or simply disappears, generating the sensation of weightlessness.
Remember that the Force of Gravity is given under the principle

Where,
G = Gravitational Universal constant
M = Mass of the planet
m = mass of the object
r = Distance from center of the planet
When the radius grows considerably the gravitational force begins to decrease.
Answer:
Cytokines
Explanation:
Cytokines are known as inflammatory molecules which are also proteinous and aid signaling of certain processes and conditions in the body.
They are also normally involved in aiding muscle building and are released when muscles experience microscopic damage which may lead to the muscles being sore.