Answer
$10$
Work Step by Step
The mass of an object can be found as:
$m=\int_a^b \rho(x) \ dx$
This implies that
$m=\int_0^2 1 dx +\int_2^4 (1+x) dx \\=|x|_0^2+\dfrac{1}{2}\times |(1+x)|_2^4 \\=2+\dfrac{1}{2} \times (25-9) \\=10$
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