When the United States shall consent thereto, the legislature, by a majority vote of the members in each house, may submit to the people the question of amending any provision of Article XXI of this constitution on compact with the United States to the extent allowed by the act of congress permitting the same, and if a majority of the qualified electors who vote upon any such amendment shall vote in favor thereof the said article shall be thereby amended accordingly. (As amended November 7, 1911.)