Since
2y + 3x = 92 (equation I)
and we know that
y + x = 35 (equation II)
Multiplying equation II by 2,
2 ( y + x = 35)
2y + 2x = 70 (equation III )
Subtracting equation III from equation I
(2y + 3x = 92) - (2y +2x = 70)
2y - 2y + 3x - 2x = 92 - 70
x = 22
Putting value of x in equation I,
2y + 3(22) = 92
2y + 66 =92
2y = 92 - 66
2y = 26
y = 26/2
y = 13
So, Robbie sold 13 boxes for $2.00