Hey there!
4/a = 5/100
CROSS MULTIPLY the FRACTIONS
4(100) = 5(a)
SIMPLIFY IT!
400 = 5a
5a = 400
DIVIDE 5 to BOTH SIDES
5a/5 = 400/5
CANCEL out: 5/5 because it give you 1
KEEP: 400/5 because it give you the x-value
NEW EQUATION: a = 400/5
SIMPLIFY IT!
a = 400 ÷ 5 / 5 ÷ 5
a = 80 / 1
a = 80 ÷ 1
a = 80
Therefore, your answer is: a = 80
Good luck on your assignment & enjoy your day!