2x + 3y + 6 +2x +5y - 3 = having trouble solving

Simonne used the following steps to simplify the given expression. 12 - 3(-2x + 4) step 1: 12 + (–3)·(–2x) + (–3)·(4) step 2: 12 + 6x + (–12) step 3: 12 + (–12) + 6x step 4: 0 + 6x step 5: 6x what property of real numbers was used to transition from step 3 to step 4? a. identity property of addition b. inverse property of addition c. associative property of addition d. commutative property of addition

For each polynomial, determine the degree and write the polynomial in descending order. a. –4x^2 – 12 + 11x^4 b. 2x^5 + 14 – 3x^4 + 7x + 3x^3

Anyone? 15m is what percent of 60m; 3m; 30m; 1.5 km?