I'll try to detail as much as possible the solution to exercise 2. Exercises 4 and 5 and basically identical: you'll have to set up a system translating the sentences to equations, and solve it. Please try to solve exercises 4 and 5 on your own (that's when you really learn!!) by mimicking how I solved exercise 2.
Let's call the three angles [tex] s,\ m,\ l [/tex] (small, medium and large, respectively). The first sentence translates to
[tex] l = s+m+10 [/tex]
The second sentence translates to
[tex] l = 3s-10 [/tex]
Since we have three unknowns, we need a third equation: this equation is implicit, because we know that the sum of the angles of a triangle is always 180 degrees:
[tex] s+m+l=180 [/tex]
So, we have the following system (rearranged in standard form):
[tex] \begin{cases} s+m-l = -10\\3s-l = 10\\s+m+l=180\end{cases} [/tex]
If you subtract the first equation from the third you get
[tex] (s+m+l)-(s+m-l) = 180-(-10) \iff 2l = 190 \iff l = 95 [/tex]
Plug this value for [tex] l [/tex] in the second equation:
[tex]3s-l = 10 \iff 3s - 95 = 10 \iff 3s = 105 \iff s = 35 [/tex]
Finally, complete to 180 to compute [tex] m [/tex]:
[tex] s+m+l=180 \iff 35+m+95 = 180 \iff m = 180-35-95 = 50 [/tex]
So, the angles are 35, 50 and 95 degrees
