1/16 + 1/8 = 3/16
1/R = 5,3333 Ohm
Plug them into the "2x8" Ohm speaker out, which uses the 4Ohm tap of the transformer.
On the back you have
1x16
1x8 (with two jack for 2 x16)
1 x 4 (with two jacks for 2x8)
I guess thát you've meant the wring thing though.