if jacob's age is 12,
12 = 3B
4 = B, so the brother is 4
how old will jacob be when he is twice as old as his brother?
Let that be x years from now. So in x years from now,
Jacob will be 12+x and his brother will be 4+x
12+x = 2(4+x)
12+x = 8+2x
4 = x
So that will be 4 years from now
So Jacob will be 12+4 or 16 and his brother will be 4+4 or 8.
Answer: Jacob will be 16.