the complement of an angle is what you add to it to get 90 degrees
if the angle is x, then the complement is y such that x+y=90
an angle is 70 less than 3 times it's complement
x=-70+3y
hmm
x+y=90
minus x both sides
y=90-x
subsitute 90-x for y
x=-70+3y
x=-70+3(90-x)
x=-70+270-3x
x=200-3x
add 4x to both sides
4x=200
divide both sides by 4
x=50
the angle is 50°