ANSWER
The smaller angle is

.EXPLANATION
Let the angles be

where y is the smaller angle.
Since they are supplementary, they will add up to 180°.
This implies that,

If one angle is 4 times the other, we can then write the following equation,

We put equation (2) into equation (1) to get,


We divide through by 5 to obtain,

This implies that,

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The answers:
x = 1
y = -5
Indefinitely many
The lines are on each other so every solution is correct
Using Pythagoras in the first question
c=

which is approximately 16.5
for the second question
we also use Pythagoras
