Exercise algebra.equations.linear.balance

Description
Solve a linear equation using only balance rules.

Derivation

3*x+21 == 10*x

⇒ algebra.equations.linear.balance.var-right-minus, term=3*x

21 == 7*x

⇒ algebra.equations.linear.balance.scale-to-one, factor=7

3 == x

⇒ algebra.equations.linear.flip

x == 3