Answer
$I_1=0.562A$
Work Step by Step
a) $I_1=I_2+I_3$
$24.0V=I_123\Omega+I_229\Omega$
$I_2=0.828A-0.793I_1$
$18.0V=I_123\Omega+I_328\Omega$
$I_3=0.643A-0.821I_1$
$I_1=0.828A-0.793I_1+0.643A-0.821I_1$
$I_1=0.562A$
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