Sarah is twice as old as his youngest brother If the difference between their ages is 15 years How old is her youngest brother?

Sarah's age is 30 years right now. Her youngest brother's age is 15 years. --- Algebraically, this results from the equations where S is Sarah's age, x her brother's age : S=2x and S-x=15, where substitution provides 2x-x = 15 and x = 15.