-0.4=g/3-0.9
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Simplify
-0.4=1/3g-0.9
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Flip
1/3g-0.9=-0.4
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Add 0.9 on each side
1/3g-0.9+0.9=-0.4+0.9
1/3g=0.5
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Multiply each side by 3
3*(1/3g)=(3)*(0.5)
g = 1.5 is your answer