When a paper is folded, its thickness doubles each time. After 1 fold, thickness = $v \times 2$. After 2 folds, thickness = $v \times 2 \times 2 = v \times 2^2$. After 10 folds, thickness = $v \times 2^{10} = 2^{10}v$. The chapter explains that the thickness doubles after each fold, so after n folds, the thickness is $v \times 2^n$.