book Maths Puzzle Numerical Ability

2(3x+1)+15=-7

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book Other Question

x^2yz^3=7^3 and xy^2=7^9 find the value of xyz. Evaluate the following to 4 decimal places. tan3.75 radians
I put down...
tan3.75(pi)
15(pi)/(divided by)4=180/(pi)
tan675-(360)
tan45=-1.0000
but i got it wrong on my test, can you show me what i did wrong?