consider the sequence -101, -91, -81, -71,
what is the 75th term in the sequence?

The sequence repeatedly increases by ten starting from the first term. The second term is 10 bigger than the previous, the third term is 10 bigger than the previous also and so on. You could write this as x, x+10, x+20, x+30...

As you can see the the term is always (n-1)10 greater than the first term. Using this the 75th term is 74*10 greater than the first term. -101+740 = 639. So the 75th term is 639