Question 1143345
You can use the formulas:
{{{ A = P[1]*( 1 + r/n )^(n*t) }}} ( compound interest )
{{{ I = P[2]*r*t }}} ( simple interest )
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{{{ P[1] = 1200 }}}
{{{ P[2] = 600 }}}
{{{ r = .2 }}}
{{{ t = 2 }}}
{{{ n = 1 }}}
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{{{ A = 1200*( 1 + .2/1 )^( 1*2) }}}
{{{ A = 1200*1.2^2 }}}
{{{ A = 1200*1.44 }}}
{{{ A = 1728 }}} 
{{{ I[1] = A - P }}}
{{{ I[1] = 1728 - 1200 }}}
{{{ I[1] = 528 }}}
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{{{ I[2] = 600*.2*1 }}}
{{{ I[2] = 120 }}}
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{{{ I[1] + I[2] = 528 + 120 }}}
{{{ I[1] + I[2] = 648 }}}
The total interest is 648
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Get a 2nd opinion if needed