Distribute 4 over (5a - 2b) to find that 4(5a - 2b) = 20a - 8b. Remember how exponent notation works? If not, get a refresher here. If we distribute something that has a variable over a quantity in parentheses that also contains that variable, we use exponent notation to keep things tidy. Probably couldn't hurt to also spray it down with a few squirts of Glass Plus. | 
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