Current Attempt in Progress

The figure shows two blocks connected by a cord $($of negligible mass$)$ that passes over a frictionless pulley $($also of negligible mass$).$ The arrangement is known as Atwood's machine. Block $1$ has mass $m_1=1\mathrm{.}9kg$; block $2$ has mass $m_2=3\mathrm{.}1kg.$ What are $($a$)$ the magnitude of the blocks' acceleration and $($b$)$ the tension in the cord?

$($a$)$ Number

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$($b$)$ Number

Units