Although there is a bit of information missing, I can answer this question in a general sense. If taxable income is $97,800, then the tax liability is $97,800 * (Tax Rate). For example, if the tax rate is %15 then the tax liability will be $97,800 * .15 = $14,670.
If taxable income increases by $21,000, then the additional tax liability in addition to the $14,670 reported earlier will be $21,00 * .15 = $3,150. Please substitute whatever tax rate is given in the original problem wherever i stated .15 or %15. This is just an arbitrary number I used because the information was missing from the problem.
