the horizontal cross section is a pentagon.
it will be the same shape as the base which is a pentagon.
step-by-step explanation: x is an even number. x+2 is the next even number, x+4 is the third even number in the set, x+6 is the fourth, x+8 is the fifth. x+x+2+x+4+x+6+x+8=100. so 5x+20=100. 100-20=5x+20-20. 80=5x. x=16.