Ni Hua is an adventurous traveler. He skydives twice in every island he visits and skydives thrice in every peninsula he visits. In the last decade, Ni Hua went skydiving a total of 45 times in the 19 islands and peninsulas that he visited. How many islands and peninsulas did Ni Hua visit?

let the number of islands visited be x and that peninsulas be y
thus,
x+y=19
⇒y=19-x.........i
if he skydives twice in islands and thrice in peninsulas, then the total number of skydives will be:
2x+3y=45.....ii

substituting i in ii we get:
2x+3(19-x)=45
2x+57-3x=45
putting like terms together we get:
2x-3x=45-57
-x=-12
therefore
x=12
and
y=19-x=19-12=7
hence the number of islands visited was 12 and that of peninsulas was 7