The Singing Hedgehog Guide to:
Algebra - Substitution 3
Here is a harder example:
Substitute the given values into the following expression:
4a + b²             a=1/5, b=-4

As before, start with the "Not thinking" line:
4x(1/5) + (-4)²        

now sort out the numbers:
4/5 + 16 = 164/5

remember that squared means times by itself so,
(-4)² = (-4)x(-4)
minus times a minus is a plus so,
(-4)x(-4) = +16
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