What must $t$t equal to make the following equation true?

$1+t=4$1+t=4

What must $k$k equal to make the following equation true?

$k+1=7$k+1=7

What must $x$x equal to make the following equation true?

$6+x=13$6+x=13

What must $j$j equal to make the following equation true?

$j+5=10$j+5=10