How to complete Line 4a and 4b on new form 1040 (for 2018) for IRA rollover and Roth conversion?

how to correctly enter on Line 4a and 4b if you did 401(K) direct rollover into traditional IRA and then did Roth conversion of some of the rolled over IRA? e.g. direct rollover of 25,000 and then12,000 Roth conversion out of those 25,000. In previous 1040 these two steps were done on different lines. Now we have a single line, Line 4(a and b). So, how to do it correctly?