First we need to find ∡PRQ. To do this we can use the fact that the sum of the interior angles of a triangle is 180°:
[tex]180=R+P+Q[/tex]
[tex]180=R+40+105[/tex]
[tex]180=R+145[/tex]
[tex]R=180-145[/tex]
[tex]R=35[/tex]
Now, we can use the fact that a strait line (like SRQ) is also 180°:
[tex]SRQ=180-R[/tex]
[tex]SRQ=180-35[/tex]
[tex]SRQ=145[/tex] °
