Step by step
The question
Question: find x when the angles on a straight line are 75° and x.
1 Use the angle fact
Angles on a straight line add up to 180°.
A straight line is half a turn.
So we add them all and make it 180: 75 + x = 180.
75 + x = 180
2 Remove the 75
We want x by itself.
The 75 is in the way.
To remove 75, we take away 75.
We do it on both sides.
Why both sides?
The = sign means both sides are the same amount.
If we change only one side, they are not the same any more.
75 and − 75 make zero.
Cross them out.
180 minus 75 is 105.
So x = 105.
The angle x is 105°.
x = 105
3 Check
Let's check: put x = 105 back and add the angles.
75 + 105 = 180
They add up to 180°.
So x = 105 is right!
Let's look back.
First: use the angle fact.
Then: remove the 75.
Last: check.
Answer
x = 105