90. In the morning, Xiao Wang rode a bike from place A to place B. At noon 12 o'clock, Xiao Li drove a car from place A to place B as well. At 1:30 PM, the distance between the two was 18 kilometers, and at 2:30 PM, the distance between them was again 18 kilometers. Xiao Li arrived at place B at 4 PM, and Xiao Wang arrived at place B at 6 PM. Xiao Wang set off in the morning at $\qquad$ o'clock.
answer: 10