Explanation:
"supplementary angles" means that together they sum up to 180 degrees. like the 2 angles when one line intersects another line.
m, k are the 2 angles
m+k = 180
m = 5k
so, when we substitute that into the first equation
5k + k = 180
6k = 180
k = 30 degrees
m = 5×30 = 150 degrees