SAT Question 5910bfff: Nonlinear Equations In One Variable And Systems Of Equations In Two Variables answer and explanation with Desmos solution

Choice A is correct. It's given that $D=T-\frac{9}{25}(100-H)$. Solving this formula for $H$ expresses the relative humidity in terms of the temperature and the dew point. Subtracting $T$ from both sides of this equation yields $D-T=-\frac{9}{25}(100-H)$. Multiplying both sides by $-\frac{25}{9}$ yields $-\frac{25}{9}(D-T)=100-H$. Subtracting $100$ from both sides yields $-\frac{25}{9}(D-T)-100=-H$. Multiplying both sides by $-1$ results in the formula $\frac{25}{9}(D-T)+100=H$.