Answer
$(-6i-9j)+(7i+7j)$
Work Step by Step
Since, we have $u=u_1+u_2$ or, $i-2j=a(2i+3j)+b(i+j)$
or, $2a+b=1; 3a+b=-2$
After solving the above two equations, we have $a=-3$
From equation $2a+b=-1 \implies 2(-3)+b=1$
or, $b=7$
Hence, $u=u_1+u_2=-3(2i+3j)+7(i+j)=(-6i-9j)+(7i+7j)$
