Solve it by Substitution

no link or website please please do step by step

Isee the amount was $90.00 then reduced to $75.00 , what is the percent ?

If the speed of an electromagnetic wave is 100,000 cm/s and its wavelength is 100 cm, what is its frequency? a) 100,000 cycles per second (hz) b) 1 × 10-3 cycles per second (hz) c) 10,000,000 cycles per second (hz) d) 1,000 cycles per second (hz)

The bake stars picked 907 apples last weekend at a local orchard they made caramel apples and sold them in the bakery in trays of 6