a]
[tex]15+x=25\\\\x=25-15\\\\x=10[/tex]
b]
[tex]7-x=-1\\\\x=7+1\\\\x=8[/tex]
c]
[tex]3-x=5\\\\x=3-5\\\\x=-2[/tex]
d]
[tex]x-16=4\\\\x=4+16\\\\x=20[/tex]
e]
[tex]3x=21 \ \ |:3\\\\x=7[/tex]
f]
[tex]x\cdot 4=36 \ \ |:4\\\\x=9[/tex]
g]
[tex]x:8=4 \ \ |\cdot8\\\\x=32[/tex]
i]
[tex]64:x=16\\\\x=64:16\\\\x=4[/tex]