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2B + 3U = 420, (1)
4B + 2U = 472. (2)
Multiply equation (1) by 2 (both sides). Keep equation (2) as is.
4B + 6U = 840, (1')
4B + 2U = 472. (2')
Now subtract equation (2') from equation (1').
You will get
4U = 840 - 472 = 368
U = 368/4 = 92 dollars. ANSWER
Solved.