I am trying to find n-dimensional Lebesgue measure of A. Let A ⊂ R n...

I am trying to find $n$-dimensional Lebesgue measure of $A$. Let $A\subset {\mathbb{R}}^n$ be a set:
$A=\{(x_1,x_2,\dots ,x_n)\in {\mathbb{R}}^n:\left(\sum _{i=1}^n|x_i|\right)\le 1\}$
1. Exact same problem. The same problem appears here:
"Let n $\ge$ 1 and n is an integer. Use Fubini's theorem to calculate the n-th Lebesgue measure of this set:
$\{(x_1,x_2,\dots ,x_n)\in {\mathbb{R}}^n:x_i\ge 0,i=1,2,\dots ,\sum _{i=1}^n{x}_i\le 1\}$"
1.1 For $n=1$, we have $0\le \lambda (A)\le 1⟹\lambda (A)\le 1$. It seems to be obvious to me.
1.2 For $n=2$, we have $0\le \lambda (A)\le 2⟹\lambda (A)\le 2$. Sqaure with $a=\sqrt{2}$
2. Similar problem. I have noticed similar problem, where A:
$A=\{(x_1,x_2,\dots ,x_n)\in {\mathbb{R}}^n:\sum _{i=1}^n|x_i|:\mathrm{\forall }|x_i|\le 1\}.$