in 10 years , a will be twice as old as b was 10 years ago . if a is now 9 years older than b , the present age of b is
"solution let b ' s present age = x years . then , a ' s present age ‹ = › ( x + 9 ) years . ∴ ( x + 9 ) + 10 = 2 ( x - 10 ) ‹ = › x + 19 = 2 x - 20 ‹ = › x = 39 . answer d"
add(add(multiply(const_2, 10), 10), 9)