Hey!
If you have two lines intersecting and you know one of the 4 angles at the intersection, you can calculate the other ones:
1. We know that angle a is 75* (please understand * as degree). Then it immediately follows that the opposing angle c is the same, so c =75* as well.
Now, as a full circle has 360*, we know that the remaining angles have to add up to
360 - a - c = 360 -75-75= 210.
So, b and d have to add up to 210 (as a term b+d =210
Now, similarly to a and c the angles b and d are opposing, hence the same. That means b=d.
We can use this in the term b+d =210. We get b+b =210, or 2b =210. Dividing by two we get b=105*. As b=d, we have d =105* as well.
Maybe try the second task as an exercise now :). If you need help, let me know.