一道GMAT数学题

一道GMAT数学题
This year Henry will save a certain amount of his
income,and he will spend the rest.Next year Henry
will have no income,but for each dollar that he saves
this year,he will have 1 + r dollars available to spend.
In terms of r,what fraction of his income should Henry
save this year so that next year the amount he has
available to spend will be equal to half the amount that
he spends this year?
for each dollar that he saves
this year,he will have 1 + r dollars available to spend.
完全不懂这句话……求解!