Asking for a different/diverse opinion

How do you model with the following variables to understand whether Spanish Government's Debt as a fraction of GDP "sustainable"? (i.e., does it explode, stay constant, or converges to zero?) Explain your (reasonable) assumptions if you take any?

GDP (constant prices of 2010)

Real GDP Growth

GDP (current prices)

Nominal GDP growth

Gov. Revenue (current prices)

Gov. Revenue/GDP

Gov Expenditure before interest rate payments (current prices)

Gov Expenditure/GDP

Primary Surplus (current prices)

Primary Surplus/GDP

Interest Rate Payments (current prices)

Fiscal Surplus (current prices)

Fiscal Surplus/GDP

Gov. Debt (current prices)

Gov. Debt/GDP