Growing coffee

Alignments to Content Standards: A-CED.A.3

The coffee variety Arabica yields about 750 kg of coffee beans per hectare, while Robusta yields about 1200 kg per hectare (reference). Suppose that a plantation has $a$ hectares of Arabica and $r$ hectares of Robusta.
1. Write an equation relating $a$ and $r$ if the plantation yields 1,000,000 kg of coffee.