Step-by-step explanation:
the sum of all angles around a point on one side of a line is always 180°.
just think about it : if there is a circle with its center in this point, then the line cuts the circle in half.
a full circle is 360°, and a half-circle is 180°.
so, now that we remember this, this means
180 = p +7 + 3p + 1 = 4p + 8
4p = 172
p = 43