Trace the procedure for deriving the IS schedule, as was done in Figure 13, for the case

Question:

Trace the procedure for deriving the IS schedule, as was done in Figure 13, for the case in which, rather than a fixed level of taxes (T), we have taxes depending on income
T = t1Y
Where t1 is the marginal income tax rate will the IS schedule for this case be steeper or flatter than when the level of taxes is fixed?