口算。 - = + =

1. 口算。
$\text{[math]}$ - $\text{[math]}$ = $\text{[math]}$ + $\text{[math]}$ = $\text{[math]}$ - $\text{[math]}$ = $\text{[math]}$ + $\text{[math]}$ =

$\text{[math]}$ + $\text{[math]}$ = $\text{[math]}$ - $\text{[math]}$ = $\text{[math]}$ + $\text{[math]}$ = $\text{[math]}$ - $\text{[math]}$ =