The answer is D, 10. 4 years ago she was 6, so William must have been 1 (1/6 of 6). In 6 years time she will be 16 (10+[4+6 years]).
It's a lot like solving equations.
3b-7 < 32
Add 7 to each side.
3b < 39
Divide by 3 on each side.
b < 13
Hope this helps :)
<span>57 boxes of detergent on the shelves in 2 minutes
</span><span>After 5 minutes, he had put 117 boxes on the shelves
117 - 57 = 60 (60 </span>boxes of detergent for 3 minutes)
60/3 = 20 (20 boxes of detergent per minute)
so
20 x 5 = 100 boxes of detergent
117 - 100 = 17 boxes
answer
17 boxes of detergent <span>were on the shelves when he started</span>
