Т. . A number composed of two digits divisible by 5 and tens digit is less than unit digit by one

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Iwant to know what 3g+5h+4g-2h is my teacher is too selfish to tell us

Ineed no it anyone can see this

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.