Question 349650
BY DEFINITION THE SUM OF COMPLEMENTARY ANGLES IS 90 DEGREES!
{{{C[1]+C[2]=90}}} 
PROBLEM STATES! {{{C[2]}}} IS {{{4*C[1]}}}
SUBSITUTE
{{{C[1]+ (4*C[1]) =90}}}
COMBINE
{{{5C[1]=90}}}
SOLVE:
{{{C[1] = 18 degrees}}} is the angle asked for
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CHECK YOUR ANSWERS!! 18+72 = 90