The area of trapezoid ABCD is 164cm2. The altitude is 8cm, AB is 10cm, and CD is 17cm. What is BC, in centimeters?
[asy]/* AMC8 2003 #21 Problem */
size(4inch,2inch);
draw((0,0)--(31,0)--(16,8)--(6,8)--cycle);
draw((11,8)--(11,0), linetype("8 4"));
draw((11,1)--(12,1)--(12,0));
label("A", (0,0), SW);
label("D", (31,0), SE);
label("B", (6,8), NW);
label("C", (16,8), NE);
label("10", (3,5), W);
label("8", (11,4), E);
label("17", (22.5,5), E);[/asy]<spanclass=′latex−bold′>(A)</span>9<spanclass=′latex−bold′>(B)</span>10<spanclass=′latex−bold′>(C)</span>12<spanclass=′latex−bold′>(D)</span>15<spanclass=′latex−bold′>(E)</span>20