Who can help me with this worksheet ! Please I really need help

The depth of a lake at a certain point, wich is a function of the distance of that point from shore, is 30 feet.

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

Solve for x and y: 217x + 131y = 913; 131x + 217y = 827