Dec 2011 q2

Please can anyone help me understand why the basis unexpired in this question of 0.18 was subtracted from (100-3.8) instead of added to get the estimated futures price for the 1st of may. My revision book from Kaplan says it should be added.

Also the answer recommends that the futures trade should be June futures price – May futures price, shouldn’t it be; now futures price – may’s futures price. The answer is contrary to what i’ve learn’t so far. please is anyone else confused about this?