The answer is:
If a proposed amendment is sent to the states for ratification, <u>Seventy-five</u> percent of states must approve it for it to become part of the Constitution.
Citing Article 5 of the Constitution of the United States of America "The Congress, whenever two-thirds of both Chambers deem it necessary, shall propose amendments to this Constitution, or, upon requisition of the Legislative Assemblies of two thirds of the various States, will convene a Convention to propose amendments, which, in any case, will be valid for all intent and purpose, as part of this Constitution, once ratified by the Legislative Assemblies of three quarters of the States, or by Conventions in three quarters of the same, according to one way or another of ratification is proposed by Congress, considering that no amendment made before the year eighteen hundred and eighty may affect in any way the first and fourth clauses of the ninth section of the first article; no State, without its consent, will be deprived of its equal suffrage in the Senate".
