For the first problem, you're making it more complicated than it is. What you want is to find the temperature at which the wind chill changes the temperature felt by at least 30 degrees less, so solve the equation for the desired change:

For the second problem, you will multiply each side (represented by a number in square feet) by the cost per square foot for that side, and then add those numbers together to determine the total cost. The trick is that the top's cost is

, whereas the bottom's cost is

.