Let the measure of ∠L be x, and let the measure of ∠S be y.
Since it is given that they are supplementary, that is, the sum of their measures is 180⁰, it follows that:

It is also given that the measure of ∠L is 36⁰ less than three times the measure of ∠S. Hence, the equation is:

The resulting system of equations to be solved is:

Solve the resulting system of equations.
Substitute the expression for x in the second equation into the first equation:

Solve the equation for y:

Substitute y=54 into the second equation:

It follows that the measure of ∠L is 126⁰ and the measure of ∠S is 54⁰.
(Remember to use 'deg' for the degree symbol as instructed).