I got this wrong. But, I figured out algebraically.

1990: M0 mined, C0 consumed. Therefore, surplus S0 = M0-C0+S_previous.

1991:M1 mined, C1 consumed. Therefore, surplus S1=M1-C1+S0.

S0>S1 means S0>M1-C1+S0. Therefore, algebraic conclusion should be C1>M1.

Dear Spittingnickels and rest of aspired-to-be someone,

Age is not important when you determined what you want to do for rest of your ife and when you know why you want to do it. I am 57. I spent whole my 25+ years in other field with highest degree you can get in that field. I am studying LSAT because I finally found what I want to do and why I pursue it. Cheer up!