All the choices are correct.
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In our base-10 number system, moving a digit one place to the left multiplies its value by 10. Moving it one place to the right multiplies its value by 1/10.
You know already that 1,000 has 10 times the value of 100, and 1/10 the value of 10,000.
−3b+2.5=4
Subtract 2.5 from both sides.
−3b+2.5−2.5=4−2.5
−3b=1.5
Divide both sides by -3.
−3b/−3 = 1.5/−3
b=−0.5
