Mike and jasmine have a combined age of 30. mike is 3 years younger than twice jasmines age. how old is mike?

Mike is 19.

If you turn the question into an equation it turns to:
J x 2 - 3 = M

So since you don’t know Jasmine’s age you would use guess and check. 8,9, and 10 didn’t work but when you put in 11:
11 x 2 - 3 = M
22 - 3 = M
19 = M

And to check your work
J + M has to equal 30 so,
11 + 19 = 30
30 = 30