What is the height of the base on the second layer from the following PIREP: OKC UA/OV OKC180010/M 1516/FL120/TP BE20/SK BKN035 TOP075/OVC095-TOPUNKN/WX FV01SM SN/TA MO4/TB MOD 050-070/RM TCU W DURC?

The height of the base on the second layer indicated in the PIREP is derived from the information provided in the report regarding the clouds. The section "SK BKN035 TOP075" indicates that the base of the broken clouds is at 3,500 feet above mean sea level (AMSL). The following segment, "OVC095-TOPUNKN," mentions overcast clouds that are at 9,500 feet AMSL, but since we are focused on the second layer, "TOP075" is crucial here as it specifies the height of the upper boundary of the broken clouds.

Therefore, when assessing the second layer, you must observe that "TOP075" means the upper limit of that layer is at 7,500 feet AMSL. Given the heights indicated in the report, the base of the layer can be inferred. Because the second layer starts at the top of the first layer (which is 7,500 feet according to the PIREP), and considering the aeronautical practice with layers typically forming below the specified ceiling, it is reasonable to conclude that the base of the next layer of clouds listed in the report—indicated as being overcast starting from 9,500 feet—begins at this