The alcohol shown is heated with concentrated acid and gives the most substituted alkene as the major product, via the most stable carbocation. How many hydrogens are on sp3 carbons directly attached to the sp2 carbons of that alkene?

The alcohol shown is 3-methylbutan-2-ol. Loss of water gives a secondary cation, which undergoes a hydride shift to the tertiary cation. Loss of a proton gives the most substituted alkene, 2-methylbut-2-ene, in which three CH3 groups are attached to the sp2 carbons. That gives 3 x 3 = 9 hydrogens (checked with RDKit).