Need a little more explanation on expanded form

3. solve by graphing: y = 2x + 6 x + y = -3

In the diagram below, tan θ = sqrt 3. what is the value of m?

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is