Step-by-step explanation:
let age of jeff be x, age of keisha be 2x(since keisha is twice as old as jeff) and age of jessica be x+4 (since jessica is 4 years older than jeff)
Now,
x+2x+x+4=60( since sum of all their ages is 60)
or 4x=60-4
or 4x=56
or x=56/4
or x=14
therefore age of jeff=14
age of keisha=2x=2×14=28
age of jessica=x+4=14+4=18