This equation has one solution.
5(r–1) + 3r =7(r + 1)
What is the solution?

R=12 is the solution

I don't know how to explain but it needs to be 20 characters

51

step-by-step explanation:

73-22=51 the   mass number minus the amount of protons gives you the amount of neutrons

a28=58

step-by-step explanation:

a1=a1+(n-1)d

a28= 4+ (28-1)2

a28=4+(27)(2)

a28=4+54

a28=58