Mr Inflexible's Utility Function Is U(x₁,x₂)= Min(x₁,x₂)

Mr. Inflexible's utility function is U(x₁,x₂) = min(x₁,x₂) . The price of x₁ is $2 including a $1 excise tax, the price of x₂ is $2, and Mr. Inflexible's budget is $120. Imagine substituting a lump- sum tax for the excise tax. If both taxes leave Mr. Inflexible on the same indifference curve, then the
Lump- sum tax is:

A) $30.
B) $10.
C) $20.
D) $50.