Hey there!!
We solve all these by the process of Substitution.
(1) 45x=180 ; x=4
... (45)(4) = 180
... 180 = 180
(YES)
(2) 420/d=30 ; d=15
... 420/15=30
... 28≠30
...420/30 = d
... d=14
(NO, d=14)
(3) 37+s=80/2 ; s=13
... 37+s=40
... 37+13=40
... 50≠40
... 37+s=40
... s=3
(NO,s=3)
(4) 52+g=45+11 ; g=3
... 52+g=56
... 52+3=56
... 55≠56
52+g=56
... g=4
(NO,g=4)
(5) 13+14=3f ; f=9
... 27 = 3f
... 27=3(9)
... 27=27
(YES)
Hope it helps!