You're given a formula and the values. Plug them in, calculate the answer. This is substitution — and it's the skill that unlocks algebra.
Example
l = 6, w = 4
What is A?
Session Length
Personal Best:
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You just used algebra.
Every time you put a number where a letter was, that's called substitution — and it's one of the most used skills in Year 7, Year 8, Year 9, GCSE and A-Level.